Do not trigger check part3 for test mute and docs PRs (#88895)

Author: breskeby

.ci/jobs.t/elastic+elasticsearch+pull-request+part-3.yml

@@ -18,6 +18,10 @@
           github-hooks: true
           status-context: elasticsearch-ci/part-3
           cancel-builds-on-update: true
+          excluded-regions:
+            - ^docs/.*
+          black-list-labels:
+            - '>test-mute'
           black-list-target-branches:
             - 6.8
             - 7.17