fixes for JENKINS-75860

[MonthyCurious]

Fixes for the JENKINS-75860 Jira issue

Testing done

passed mvn clean verify
executed mvn spotless:apply

[MarkEWaite]

Thanks for the pull request!

Needs tests that show the problem before the change and confirm the problem is fixed by the change. The current test that invokes setSubmoduleUrl then calls getSubmoduleUrl to confirm that the set happened.

This change is moving the location that is written and read. That is good, because the test passes, but the test does not confirm that the rest of the code is functional with that change.

[MonthyCurious]

I added more info to the Jira.

Since the error is only encountered when .git/config and .gitmodules are out of sync (as are mine), I think that unifying the git commands (either use -f .gitmodules consistently everywhere or nowhere) would be good but nothing pressing.

I know the problem and can fix my git files. Please handle this PR and the associated Jira as you like.