[SPARK-55831][FOLLOWUP] Fix Maven CI by replacing with dummy SPARK_HOME in test

[pan3793]

What changes were proposed in this pull request?

Create a dummy SPARK_HOME for test, so that the YARN test won't depend on assembly package.

Why are the changes needed?

- YARN AM JavaOptions *** FAILED ***
  java.lang.IllegalStateException: Library directory '/home/runner/work/spark/spark/assembly/target/scala-2.13/jars' does not exist; make sure Spark is built.
  at org.apache.spark.launcher.CommandBuilderUtils.checkState(CommandBuilderUtils.java:230)
  at org.apache.spark.launcher.CommandBuilderUtils.findJarsDir(CommandBuilderUtils.java:320)
  at org.apache.spark.launcher.YarnCommandBuilderUtils$.findJarsDir(YarnCommandBuilderUtils.scala:36)
  at org.apache.spark.deploy.yarn.Client.prepareLocalResources(Client.scala:711)
  at org.apache.spark.deploy.yarn.Client.prepareLocalResources(Client.scala:529)
  at org.apache.spark.deploy.yarn.Client.createContainerLaunchContext(Client.scala:1042)
  at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
  at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.base/java.lang.reflect.Method.invoke(Method.java:569)
  ...

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Pass both Maven and SBT CI.

Was this patch authored or co-authored using generative AI tooling?

No.

[LuciferYang]

I think we still need to implement more fine-grained control. Some modules have their test sequences prior to the assembly module, and we should ensure that these tests can be conducted without relying on assembly. At the least, we should have a mechanism to inspect, skip, and notify that enabling these tests requires assembly(such as assume).

[pan3793]

I switched to a simple approach that makes the test not depend on the assembly package, so we don't need to worry about this case.

[pan3793]

Maven GHA passed https://github.com/pan3793/spark/actions/runs/22757891403/job/66006942452