Merge branch 'docs-update-smoke-test-list' into 'master'

Add issue user mentions to list of smoke tests

See merge request gitlab-org/gitlab!17025

doc/development/testing_guide/smoke.md

@@ -12,6 +12,7 @@ Currently, our suite consists of this basic functionality coverage:
 - Project simple creation
 - Project creation with Auto-DevOps enabled
 - Issue creation
+- Issue user mentions
 - Merge Request creation
 - Snippet creation