[SPARK-54476][PYTHON][TEST] Add coverage test for try_mod

[fallintoplace]

What changes were proposed in this pull request?

This PR adds PySpark SQL function coverage for try_mod in test_functions.py. The test covers column-name operands, Column plus literal operands, and division by zero returning null.

Why are the changes needed?

SPARK-54476 tracks adding try_mod coverage in test_functions.py. This adds direct coverage for the PySpark function wrapper.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

env JAVA_HOME=/opt/homebrew/opt/openjdk PATH=/opt/homebrew/opt/openjdk/bin:$PATH ./build/mvn -DskipTests package
env JAVA_HOME=/opt/homebrew/opt/openjdk PATH=/opt/homebrew/opt/openjdk/bin:$PATH OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES python3 python/run-tests.py --testnames "pyspark.sql.tests.test_functions FunctionsTests.test_try_mod_function" --python-executables python3
git diff --check
python3 -m py_compile python/pyspark/sql/tests/test_functions.py

Was this patch authored or co-authored using generative AI tooling?

Generated-by: GPT-5.5 xhigh

[zhengruifeng]

this seems already been tested as a doc-test

https://github.com/apache/spark/blob/master/python/pyspark/sql/functions/builtin.py#L762-L774

[fallintoplace]

Good point @zhengruifeng, thanks. I missed that the main try_mod behavior is already covered by the doctest. The only additional coverage here is the Column + literal path, which is probably too small to justify a separate test. I will close this PR unless you think explicit coverage in test_functions.py is still useful for SPARK-54476.