Fix mergeable.yml multi-line string syntax to fix invalid yaml parse error.

PiperOrigin-RevId: 492313296

.github/workflows/mergeable.yml

@@ -7,8 +7,9 @@ mergeable:
             message: 'Pull request marked not mergeable'
         - must_include:
             regex: 'mergeable:force-allow'
-            message: 'Pull requests should not be merged directly and should instead '
-              'be handled by Copybara.\n\n'
-              'To enable Github merges, add the `mergeable:force-allow` label. This should almost '
-              'never be used except for releases or as a break glass measure '
-              'after discussing with the team.'
+            message: 'Pull requests should not be merged directly and should instead
+              be handled by Copybara.
+
+              To enable Github merges, add the `mergeable:force-allow` label.
+              This should almost never be used except for releases or as a break glass measure
+              after discussing with the team.'