[SPARK-36166][TESTS][FOLLOWUP] Add BLOCK_SCALA_VERSION to sparktestss…

…upport/__init__.py

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

This is a followup PR for SPARK-36166 (#33411), which adds `BLOCK_SCALA_VERSION` to `sparktestssupport/__init__.py`.

### Why are the changes needed?

The following command fails due to the definition is missing.
```
SCALA_PROFILE=scala2.12 dev/run-tests.py
```

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

No.

### How was this patch tested?

The command shown above works.

Closes #33421 from sarutak/followup-SPARK-36166.

Authored-by: Kousuke Saruta <sarutak@oss.nttdata.com>
Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>

dev/sparktestsupport/__init__.py

@@ -34,5 +34,6 @@
     "BLOCK_JAVA_STYLE": 21,
     "BLOCK_BUILD_TESTS": 22,
     "BLOCK_PYSPARK_PIP_TESTS": 23,
+    "BLOCK_SCALA_VERSION": 24,
     "BLOCK_TIMEOUT": 124
 }