Merge branch 'jk/ci-retire-allow-ref'

CI update.

* jk/ci-retire-allow-ref:
  ci: deprecate ci/config/allow-ref script
  ci: allow branch selection through "vars"

Author: gitster

.github/workflows/main.yml

@@ -21,6 +21,7 @@ concurrency:
 jobs:
   ci-config:
     name: config
+    if: vars.CI_BRANCHES == '' || contains(vars.CI_BRANCHES, github.ref_name)
     runs-on: ubuntu-latest
     outputs:
       enabled: ${{ steps.check-ref.outputs.enabled }}${{ steps.skip-if-redundant.outputs.enabled }}
@@ -43,10 +44,13 @@ jobs:
         name: check whether CI is enabled for ref
         run: |
           enabled=yes
-          if test -x config-repo/ci/config/allow-ref &&
-             ! config-repo/ci/config/allow-ref '${{ github.ref }}'
+          if test -x config-repo/ci/config/allow-ref
           then
-            enabled=no
+            echo "::warning::ci/config/allow-ref is deprecated; use CI_BRANCHES instead"
+            if ! config-repo/ci/config/allow-ref '${{ github.ref }}'
+            then
+              enabled=no
+            fi
           fi
 
           skip_concurrent=yes

ci/config/README

@@ -0,0 +1,14 @@
+You can configure some aspects of the GitHub Actions-based CI on a
+per-repository basis by setting "variables" and "secrets" from with the
+GitHub web interface. These can be found at:
+
+  https://github.com/<user>/git/settings/secrets/actions
+
+The following variables can be used:
+
+ - CI_BRANCHES
+
+   By default, CI is run when any branch is pushed. If this variable is
+   non-empty, then only the branches it lists will run CI. Branch names
+   should be separated by spaces, and should use their shortened form
+   (e.g., "main", not "refs/heads/main").