ci: prioritize labelling pull requests based on their title rather than their commits

I think this will be better for most pull requests since conventional commits tends to mean either applying at the pull request level or only ever doing one commit; in practical terms, this means we can use cc in the context of a pull requests commits without getting both the "enhancement" and "bug" label.

Really it probably makes sense to skip checking commits in most cases or even throw/post an error, but for now I've not done that because I expect the fallback to be triggered by external contributors and this workflow currently will only run when a new change it pushed; we could change that but given how stable we are these days I'm not going to do that for now.

jest-community / eslint-plugin-jest

ci: prioritize labelling pull requests based on their title rather than their commits #1564