[CI] Fix for multiple diffs in split renderer tests

The added split renderer tests to ivas-conformance add DIFF commands on separate lines instead of separated with ; as intended. This creates a race-condition in the test_26252.py which may fail in case the output file is not created before the comparison is run.

This is a small patch to scripts/parse_commands.py, used in the ivas-conformance and ivas-conformance-linux jobs.