ci: allow opt-out of changelog lint for internal changes

[thomaseizinger]

Description

We introduced a lint in #4620 that ensures the changelog is updated when we touch a certain crate. This however leads to many "false-positives" where a change to the source code is not actually worth mentioning in the changelog.

To opt out of this change, this patch adds a condition to the job that checks for a internal:$crate label and if that is applied, it doesn't run the lint.

Notes & open questions

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• A changelog entry has been made in the appropriate crates

[thomaseizinger]

Opening this as a an idea how we could resolve the changelog lint problem. It will result in a fair few labels over time but I think by namespacing them, they should all be easier to find still.

[thomaseizinger]

Merging to unblock CI of other PRs.