i#4953 ubuntu20: Explicily invoke python2 for clang-format-diff

Locates python2 and uses it to invoke clang-format-diff for 6.0, to support running that old version on Ubuntu 20.

Issue: #4953 (closed)

This permanently updates the clang-format job to ubuntu-20.04.

Windows failures are the sourceforage server outages also hit here !5094 (merged)

requested review from @abhinav92003

approved this merge request

Merged by: derekbruening at 2021-09-16 14:39:00 UTC

closed