Attach "needs CLC feedback" label to all MRs touching testsuite/tests/interface-stability

Could GitLab attach needs CLC feedback label to any MR which touches testsuite/tests/interface-stability?

Motivation: I spotted !12741 before it was merged, but we might be less lucky next time.

A low-tech solution is to add @core-libraries to CODEOWNERS of testsuite/tests/interface-stability, but label would be much better.

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