Do not cancel PRs for PR validity checks (project-chip#37026)

Since validity checks can be fixed without commits, cancelling
PRs for them is not useful.

Author: andy31415

.github/workflows/cancel_workflows_for_pr.yaml

@@ -49,5 +49,4 @@ jobs:
                     --require "Lint Code Base" \
                     --require "ZAP"            \
                     --require "Run misspell"   \
-                    --require "PR validity"    \
                     --max-pr-age-minutes 20