`changelog-check` does not exclude `test/` and `tests/`

The `no-changelog` label had to be added to a [PR](https://github.com/MetaMask/core/pull/7001#issuecomment-3492920205) recently because it seems that while the `changelog-check` workflow excludes changes to `.test.ts` files, it does not exclude changes to `test/` and `tests/`. We should do that.

Start by locating the changelog-check workflow and inspect how it currently excludes .test.ts files. Update the workflow so changes under test/ and tests/ receive the same exclusion, then run the workflow's available checks or validate it against a pull request containing only test changes.

Written by the indexing model from the issue text.