fix(runfiles): support bzlmod repo mappings

[jbedard]

It seems like the packages/runfiles/tests have not been run for quite some time and can't be run in their current form. I've added those tests rules_js in https://github.com/aspect-build/rules_js/pull/1895 and I've been testing there where tests were failing with bzlmod which this PR fixes.

PR Checklist

Please check if your PR fulfills the following requirements:

• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• [x] Bugfix
• [ ] Feature (please, look at the "Scope of the project" section in the README.md file)
• [ ] Code style update (formatting, local variables)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] CI related changes
• [ ] Documentation content changes
• [ ] Other... Please describe:

What is the current behavior?

Issue Number: #3714

What is the new behavior?

Does this PR introduce a breaking change?

• [ ] Yes
• [ ] No

Other information