ci: run PR labeler after the add_initial_labels action, add label cases

[timvaillancourt]

Description

This PR moves the auto labeler to run sequentially after another job that edits labels, in a smarter place in the workflow files (thanks @mhamza15)

This will cause the auto-labeling to move to here (where line points)

Related Issue(s)

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

AI Disclosure

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

• Apply the release notes (needs details) label if users need to know about this change.
• New features should be documented.
• There should be some code comments as to why things are implemented the way they are.
• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• Is this flag really necessary?
• Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
• If the workflow needs to be marked as required, the maintainer team must be notified.

Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[mhamza15]

I think we'd rather have this in the PR opened tasks workflow: https://github.com/vitessio/vitess/blob/main/.github/workflows/pr_opened_tasks.yml.

[timvaillancourt]

I think we'd rather have this in the PR opened tasks workflow: https://github.com/vitessio/vitess/blob/main/.github/workflows/pr_opened_tasks.yml.

@mhamza15 yes, that's what I meant to do 👍. Updated