[SPARK-32408][BUILD] Enable crossPaths back to prevent side effects

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

This PR proposes to enable `corssPaths` back for now to match with the build as it was.
It still indeterministically doesn't run JUnit tests given my observation, and this PR basically reverts the partial fix from #29057.

See also #29205 for the full context.

### Why are the changes needed?

To prevent the side effects from crossPaths such as SPARK_PREPEND_CLASSES or tests that run conditionally if the test classes are present in PySpark.

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

No, dev-only.

### How was this patch tested?

Manually tested:

```bash
build/sbt -Phadoop-2.7 -Phive -Phive-2.3 -Phive-thriftserver -DskipTests clean test:package
./python/run-tests --python-executable=python3 --testname="pyspark.sql.tests.test_dataframe QueryExecutionListenerTests"
```

Closes #29218 from HyukjinKwon/SPARK-32408-1.

Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

project/SparkBuild.scala

@@ -1032,8 +1032,6 @@ object TestSettings {
     // Show full stack trace and duration in test cases.
     testOptions in Test += Tests.Argument("-oDF"),
     testOptions in Test += Tests.Argument(TestFrameworks.JUnit, "-v", "-a"),
-    // Required to detect Junit tests for each project, see also https://github.com/sbt/junit-interface/issues/35
-    crossPaths := false,
     // Enable Junit testing.
     libraryDependencies += "com.novocode" % "junit-interface" % "0.11" % "test",
     // `parallelExecutionInTest` controls whether test suites belonging to the same SBT project