only run core4 check on non-draft PRs

[johnduffell]

after the outcome of discussions relating to guardian/support-service-lambdas#3280
on this thread https://chat.google.com/room/AAAAag0I08g/XFliRTXYAzQ/XFliRTXYAzQ?cls=10

This PR makes the workflow only run on PRs that are not draft

Tested using this PR guardian/support-service-lambdas#3280 :

and when it's marked ready for review

The only issue is you need to add "ready_for_review" as a trigger as seen in the above PR
https://github.com/guardian/support-service-lambdas/pull/3280/files#diff-121fb0d715d38abf3163eb63b4ce94e1a9e6fa685f89d8b61d9b8eb5e31cbb81R6

[Copilot]

Pull request overview

This PR modifies the GitHub Actions workflow to only enforce the required label check on pull requests that target the default branch, avoiding unnecessary checks on PRs targeting other branches (e.g., feature branches).

Key Changes:

• Added a conditional check to the workflow job to filter PRs by their target branch

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[Copilot]

The comparison will always fail because github.event.repository.default_branch returns the branch name as a string (e.g., 'main'), but github.event.pull_request.base.ref also returns a string. However, the correct way to reference the default branch name is github.event.repository.default_branch without any further qualification. The condition should compare the base ref name directly: github.event.pull_request.base.ref == github.event.repository.default_branch.\n\nActually, upon closer inspection, this syntax is correct for the comparison. However, ensure this works as intended by testing, as the typical pattern seen is to use string literals or to be explicit about what's being compared.

Suggested change

	if: github.event.pull_request.base.ref == github.event.repository.default_branch
	if: github.ref_name == github.event.repository.default_branch