fix(ci): restrict PR checklist by author

The existing check reacts to whoever performs an action, so pushing a
commit to a PR opened by the konflux bot will trigger the checklist
validation. This is not a huge deal, but since MintMaker PRs have
predefined descriptions, we should never attempt to validate them.

With this change we restrict the validation to PRs that are not opened
by konflux bot.

For an example of a MintMaker PR running the checklist validation test
after a push from another user see #679.

Author: Molter73

.github/workflows/pr-checklist.yml

@@ -15,7 +15,7 @@ jobs:
     if: github.event.pull_request.draft == false
     steps:
       - name: Verify PR Checklist is Complete
-        if: github.actor != 'red-hat-konflux[bot]'
+        if: github.event.pull_request.user.login != 'red-hat-konflux[bot]'
         env:
           PR_BODY: ${{ github.event.pull_request.body }}
         run: |
@@ -30,6 +30,6 @@ jobs:
           fi
 
       - name: Skip check for MintMaker
-        if: github.actor == 'red-hat-konflux[bot]'
+        if: github.event.pull_request.user.login  == 'red-hat-konflux[bot]'
         run: |
           echo "MintMaker PRs are exempted from this check"