[SPARK-38084][TESTS] Support SKIP_PYTHON and SKIP_R in `run-tests…

….py`

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

This PR aims to support `SKIP_PYTHON` and `SKIP_R` in `run-tests.py` like `SKIP_MIMA` and `SKIP_UNIDOC`.

### Why are the changes needed?

This is helpful to setup CIs.

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

No.

### How was this patch tested?

Manually.
```
SKIP_PYTHON=1 SKIP_R=1 dev/run-tests.py
```

Closes apache#35381 from dongjoon-hyun/SPARK-38084.

Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
(cherry picked from commit 6347b9d)
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
(cherry picked from commit 42b3c96)

dev/run-tests.py

@@ -760,13 +760,13 @@ def main():
     run_scala_tests(build_tool, extra_profiles, test_modules, excluded_tags, included_tags)
 
     modules_with_python_tests = [m for m in test_modules if m.python_test_goals]
-    if modules_with_python_tests:
+    if modules_with_python_tests and not os.environ.get("SKIP_PYTHON"):
         run_python_tests(
             modules_with_python_tests,
             opts.parallelism,
             with_coverage=os.environ.get("PYSPARK_CODECOV", "false") == "true")
         run_python_packaging_tests()
-    if any(m.should_run_r_tests for m in test_modules):
+    if any(m.should_run_r_tests for m in test_modules) and not os.environ.get("SKIP_R"):
         run_sparkr_tests()