Make label checks more dynamic

[diehlbw]

Overview

Closes #22

Description of changes

Use gh api to request labels dynamically instead of using the cached list that requires an event (commit) to renew. Split changelog workflow into two jobs; could not find a method for short-circuiting success within a job.

Note: this method is intentionally requiring manual retry, and NOT triggering off of label changes

Suggested testing-
As a step 0, I'm intentionally NOT setting labels prior to PR creation.
Tests can add and remove labels on this PR, then manually rerun the specific workflow.
Verify that the second job runs and is skipped depending on the skip-changelog label.
Before merge, update labels and drop the second commit to verify the push event also behaves correctly

Author Checklist

• [ ] Linting passes; run early with pre-commit hook.
• [ ] Tests added for new code and issue being fixed.
• [ ] Added type annotations and full numpy-style docstrings for new methods.
• [ ] Draft your news fragment in new changelog/ISSUE.TYPE.rst files; see changelog/README.md.

[diehlbw]

Initial run 'successfully' set needs_entry.
Rerun after setting a different label, timed out on first attempt(?) then set it correctly.