[SPARK-32714][FOLLOW-UP][PYTHON] Address pyspark.install typing errors

[zero323]

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
31a16fb

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
  

[zero323]

cc @HyukjinKwon

[SparkQA]

Test build #129136 has finished for PR 29878 at commit fb89746.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Kubernetes integration test starting
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/33752/

[SparkQA]

Kubernetes integration test status success
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/33752/

[HyukjinKwon]

Thanks, @zero323. Merged to master.