### What changes were proposed in this pull request?
This PR adds two `type: ignores`, one in `pyspark.install` and one in related tests.
### Why are the changes needed?
To satisfy MyPy type checks. It seems like we originally missed some changes that happened around merge of
31a16fbb40
```
python/pyspark/install.py:30: error: Need type annotation for 'UNSUPPORTED_COMBINATIONS' (hint: "UNSUPPORTED_COMBINATIONS: List[<type>] = ...") [var-annotated]
python/pyspark/tests/test_install_spark.py:105: error: Cannot find implementation or library stub for module named 'xmlrunner' [import]
python/pyspark/tests/test_install_spark.py:105: note: See https://mypy.readthedocs.io/en/latest/running_mypy.html#missing-imports
```
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
- Existing tests.
- MyPy tests
```
mypy --show-error-code --no-incremental --config python/mypy.ini python/pyspark
```
Closes#29878 from zero323/SPARK-32714-FOLLOW-UP.
Authored-by: zero323 <mszymkiewicz@gmail.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
c65b64552f