[SPARK-38966][CI] Allow fork branches to be in-sync with upstream master

[EnricoMi]

What changes were proposed in this pull request?

Make git commit in .github/workflows/build_and_test.yml work with empty commits by adding --allow-empty to the command.

Why are the changes needed?

Whenever I sync my fork master from upstream Apache master, CI fails:

From https://github.com/G-Research/spark
 * branch                  master     -> FETCH_HEAD
Already up to date. (nothing to squash)
On branch master
Your branch is up to date with 'origin/master'.

nothing to commit, working tree clean
Error: Process completed with exit code 1.

Since my fork master is without changes, the git commit fails. This is annoying.

The same issue makes the scheduled build and test workflow fail multiple times a day.

Does this PR introduce any user-facing change?

No, this is CI only.

How was this patch tested?

Tested git commit --allow-empty with no changes on command line.

[AmplabJenkins]

Can one of the admins verify this patch?

[HyukjinKwon]

@EnricoMi I think the change is good. Mind filing a JIRA?

[EnricoMi]

Done

[HyukjinKwon]

Merged to master.

[EnricoMi]

Thanks!

[EnricoMi]

Scheduled build-and-test workflow is not failing in forks any more, thanks: https://github.com/G-Research/spark/runs/6095625654?check_suite_focus=true