Merge branch 'docs-vale-merge-conflict-test' into 'master'

Create vale test for unresolved merge conflicts

Closes #219168

See merge request gitlab-org/gitlab!33125

doc/.vale/gitlab/MergeConflictMarkers.yml

+---
+# Error: gitlab.MergeConflictMarkers
+#
+# Checks for the presence of merge conflict markers.
+#
+# For a list of all options, see https://errata-ai.github.io/vale/styles/
+extends: existence
+message: 'Merge conflict marker "%s" found.'
+link: https://docs.gitlab.com/ee/development/code_review.html#merging-a-merge-request
+level: error
+scope: raw
+raw:
+  - '\n<<<<<<< .+\n|\n=======\n|\n>>>>>>> .+\n'