Temporarily let ci.yml run on "run-ci" branches' pull_request

So far, the forthcoming experiment using `dynamic-uses` has been
the only need to for this. So my plan is not to propose this change
upstream, but only to use it for that experiment, at least for now.

Author: EliahKagan

.github/workflows/ci.yml

@@ -11,6 +11,8 @@ on:
   pull_request:
     branches:
       - main
+      - 'run-ci/**'     # FIXME: Remove after testing.
+      - '**/run-ci/**'  # FIXME: Remove after testing.
   workflow_dispatch:
 
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