[SPARK-49221][BUILD] Fix sbt compilation warnings related to `Regular…

… tasks always evaluate task dependencies (.value) regardless of if expressions`

### What changes were proposed in this pull request?
This PR changes to use `taskDyn` to dynamically define `task` based on the value of `moduleName.value.contains("assembly")` in order to fix compilation warnings:

```
[warn] /home/runner/work/spark/spark/project/SparkBuild.scala:1554:77: value lookup of `/` inside an `if` expression
[warn]
[warn] problem: `/.value` is inside an `if` expression of a regular task.
[warn]   Regular tasks always evaluate task dependencies (`.value`) regardless of `if` expressions.
[warn] solution:
[warn]   1. Use a conditional task `Def.taskIf(...)` to evaluate it when the `if` predicate is true or false.
[warn]   2. Or turn the task body into a single `if` expression; the task is then auto-converted to a conditional task.
[warn]   3. Or make the static evaluation explicit by declaring `/.value` outside the `if` expression.
[warn]   4. If you still want to force the static lookup, you may annotate the task lookup with `sbtUnchecked`, e.g. `(/.value: sbtUnchecked)`.
[warn]   5. Add `import sbt.dsl.LinterLevel.Ignore` to your build file to disable all task linting.
[warn]
[warn]         val replClasspathes = (LocalProject("connect-client-jvm") / Compile / dependencyClasspath)
[warn]                                                                             ^
[warn] one warning found
```

### Why are the changes needed?
Fix compilation warnings in the GA compilation log

- https://github.com/apache/spark/actions/runs/10365742495/job/28693551621

<img width="880" alt="image" src="https://github.com/user-attachments/assets/e1a94017-cde3-4d55-9a67-197bb2f3e484">

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
- Pass Github Actions
- Check the GA compilation log, and ensure there are no warnings as mentioned above.
- Manual check

```
build/sbt clean assembly/package -Phive
ls -l assembly/target/scala-2.13/jars/connect-repl
```

Before and after this PR, the content under the `assembly/target/scala-2.13/jars/connect-repl ` directory remains consistent.

### Was this patch authored or co-authored using generative AI tooling?
No

Closes apache#47739 from LuciferYang/dynTask.

Authored-by: yangjie01 <yangjie01@baidu.com>
Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>

project/SparkBuild.scala

@@ -1549,30 +1549,37 @@ object CopyDependencies {
 
       // Here we get the full classpathes required for Spark Connect client including
       // ammonite, and exclude all spark-* jars. After that, we add the shaded Spark
-      // Connect cleint assembly manually.
-      if (moduleName.value.contains("assembly")) {
-        val replClasspathes = (LocalProject("connect-client-jvm") / Compile / dependencyClasspath)
-          .value.map(_.data).filter(_.isFile())
-        val scalaBinaryVer = SbtPomKeys.effectivePom.value.getProperties.get(
-          "scala.binary.version").asInstanceOf[String]
-        val sparkVer = SbtPomKeys.effectivePom.value.getProperties.get(
-          "spark.version").asInstanceOf[String]
-        val destDir = new File(dest, "connect-repl").toPath
-        Files.createDirectories(destDir)
-
-        val sourceAssemblyJar = Paths.get(
-          BuildCommons.sparkHome.getAbsolutePath, "connector", "connect", "client",
-          "jvm", "target", s"scala-$scalaBinaryVer", s"spark-connect-client-jvm-assembly-$sparkVer.jar")
-        val destAssemblyJar = Paths.get(destDir.toString, s"spark-connect-client-jvm-assembly-$sparkVer.jar")
-        Files.copy(sourceAssemblyJar, destAssemblyJar, StandardCopyOption.REPLACE_EXISTING)
-
-        replClasspathes.foreach { f =>
-          val destFile = Paths.get(destDir.toString, f.getName)
-          if (!f.getName.startsWith("spark-")) {
-            Files.copy(f.toPath, destFile, StandardCopyOption.REPLACE_EXISTING)
-          }
+      // Connect client assembly manually.
+      Def.taskDyn {
+        if (moduleName.value.contains("assembly")) {
+          Def.task {
+            val replClasspathes = (LocalProject("connect-client-jvm") / Compile / dependencyClasspath)
+              .value.map(_.data).filter(_.isFile())
+            val scalaBinaryVer = SbtPomKeys.effectivePom.value.getProperties.get(
+              "scala.binary.version").asInstanceOf[String]
+            val sparkVer = SbtPomKeys.effectivePom.value.getProperties.get(
+              "spark.version").asInstanceOf[String]
+            val dest = destPath.value
+            val destDir = new File(dest, "connect-repl").toPath
+            Files.createDirectories(destDir)
+
+            val sourceAssemblyJar = Paths.get(
+              BuildCommons.sparkHome.getAbsolutePath, "connector", "connect", "client",
+              "jvm", "target", s"scala-$scalaBinaryVer", s"spark-connect-client-jvm-assembly-$sparkVer.jar")
+            val destAssemblyJar = Paths.get(destDir.toString, s"spark-connect-client-jvm-assembly-$sparkVer.jar")
+            Files.copy(sourceAssemblyJar, destAssemblyJar, StandardCopyOption.REPLACE_EXISTING)
+
+            replClasspathes.foreach { f =>
+              val destFile = Paths.get(destDir.toString, f.getName)
+              if (!f.getName.startsWith("spark-")) {
+                Files.copy(f.toPath, destFile, StandardCopyOption.REPLACE_EXISTING)
+              }
+            }
+          }.dependsOn(LocalProject("connect-client-jvm") / assembly)
+        } else {
+          Def.task {}
         }
-      }
+      }.value
     },
     (Compile / packageBin / crossTarget) := destPath.value,
     (Compile / packageBin) := (Compile / packageBin).dependsOn(copyDeps).value