fix(script): Store cargo script lockfiles in build-dir

This is more conceptually correct but if people decide to share a
`build-dir` across projects,
it will wreak havoc on their cargo script builds.

Author: epage

src/cargo/core/workspace.rs

@@ -668,7 +668,7 @@ impl<'gctx> Workspace<'gctx> {
 
     fn default_lock_root(&self) -> Filesystem {
         if self.root_maybe().is_embedded() {
-            self.target_dir()
+            self.build_dir()
         } else {
             Filesystem::new(self.root().to_owned())
         }