[SPARK-39657][YARN] YARN AM client should call the non-static setTokensConf method

### What changes were proposed in this pull request?

This fixes a bug in the original SPARK-37205 PR, where we treat the method `setTokensConf` as a static method, but it should be non-static instead.

### Why are the changes needed?

The method `setTokensConf` is non-static so the current code will fail:
```
06/29/2022 - 17:28:16  - Exception in thread "main" java.lang.IllegalArgumentException: object is not an instance of declaring class
06/29/2022 - 17:28:16  - at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
06/29/2022 - 17:28:16  - at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
06/29/2022 - 17:28:16  - at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
06/29/2022 - 17:28:16  - at java.base/java.lang.reflect.Method.invoke(Method.java:566)
```

### Does this PR introduce _any_ user-facing change?

No

### How was this patch tested?

Manually tested this change internally and it now works.

Closes #37050 from sunchao/SPARK-39657.

Authored-by: Chao Sun <sunchao@apple.com>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
(cherry picked from commit 6624d91)
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

Author: sunchao

resource-managers/yarn/src/main/scala/org/apache/spark/deploy/yarn/Client.scala

@@ -391,7 +391,7 @@ private[spark] class Client(
           throw new SparkException(s"Cannot find setTokensConf method in ${amContainer.getClass}." +
               s" Please check YARN version and make sure it is 2.9+ or 3.x")
       }
-      setTokensConfMethod.invoke(ByteBuffer.wrap(dob.getData))
+      setTokensConfMethod.invoke(amContainer, ByteBuffer.wrap(dob.getData))
     }
   }