Fix repo mapping for bzlmod detection

[Mivr]

PR Checklist

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

@bazel/runfiles does not work with non-bzlmod when a _repo_mapping file exists

Issue Number: #3797

What is the new behavior?

The parsing code handles old and new repo_mapping syntax

Does this PR introduce a breaking change?

• [ ] Yes
• [ x] No

[aspect-workflows[bot]]

Test

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