ICU-23056 Run CI for exhaustive tests on PRs that update resource files

[echeran]

In order to better prevent issues stemming from exhaustive tests that assert the consistency / conformance of locale data (example), this CI will automatically run exhaustive tests on the PRs that update locale data via resource files.

Currently, the ICU4J / ICU4C tests that run on every push to a PR or merge to main don't test the full set of features that are covered by exhaustive tests. Meanwhile, exhaustive tests do not run on all PRs or merges to main, but instead on a periodic basis on main and on every push to a maintenance branch.

So in total, this PR carves out and enables a narrowly defined middle ground such that we get the full set of test coverage on PRs before we merge, with the knowledge that locale data isn't updated often, but when it is updated, it can affect more tests and functionality than what is covered by the quick running tests that we run on every PR commit push.

Checklist

• Required: Issue filed: ICU-23056
• Required: The PR title must be prefixed with a JIRA Issue number. Example: "ICU-1234 Fix xyz"
• Required: Each commit message must be prefixed with a JIRA Issue number. Example: "ICU-1234 Fix xyz"
• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable

[mihnita]

Thank you, lgtm

[mihnita]

Sorry, I tried to approve from the GitHub Android app.
And didn't quite work.
But now I am in the buss, and I can do it from my laptop.

Thank you,
M