incorrect caching: classified PR as new_module even though the module it modifies was merged earlier

[felixfontein]

I today merged a new module (ansible/ansible#50622), then rebased two PRs to current devel, and included modifications for these new modules as well. Afterwards, ansibot adds new_module and new_plugin labels to the PR.

Affected PRs: ansible/ansible#51939, ansible/ansible#51999

[felixfontein]

Another case: ansible/ansible#56103, ansible/ansible#56186

[felixfontein]

In this new case, the new PR adds another module and modifies the previously merged module, and gets the "this PR contains more than one new module" error.