ci: deprecate ci/config/allow-ref script

Now that we have the CI_BRANCHES mechanism, there is no need for anybody
to use the ci/config/allow-ref mechanism. In the long run, we can
hopefully remove it and the whole "config" job, as it consumes CPU and
adds to the end-to-end latency of the whole workflow. But we don't want
to do that immediately, as people need time to migrate until the
CI_BRANCHES change has made it into the workflow file of every branch.

So let's issue a warning, which will appear in the "annotations" section
below the workflow result in GitHub's web interface. And let's remove
the sample allow-refs script, as we don't want to encourage anybody to
use it.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.github/workflows/main.yml

@@ -31,10 +31,13 @@ jobs:
         name: check whether CI is enabled for ref
         run: |
           enabled=yes
-          if test -x config-repo/ci/config/allow-ref &&
+          if test -x config-repo/ci/config/allow-ref
-             ! config-repo/ci/config/allow-ref '${{ github.ref }}'
           then
-            enabled=no
+            echo "::warning::ci/config/allow-ref is deprecated; use CI_BRANCHES instead"
+            if ! config-repo/ci/config/allow-ref '${{ github.ref }}'
+            then
+              enabled=no
+            fi
           fi
 
           skip_concurrent=yes

ci/config/allow-ref.sample

@@ -1,27 +0,0 @@
-#!/bin/sh
-#
-# Sample script for enabling/disabling GitHub Actions CI runs on
-# particular refs. By default, CI is run for all branches pushed to
-# GitHub. You can override this by dropping the ".sample" from the script,
-# editing it, committing, and pushing the result to the "ci-config" branch of
-# your repository:
-#
-#   git checkout -b ci-config
-#   cp allow-ref.sample allow-ref
-#   $EDITOR allow-ref
-#   git add allow-ref
-#   git commit -am "implement my ci preferences"
-#   git push
-#
-# This script will then be run when any refs are pushed to that repository. It
-# gets the fully qualified refname as the first argument, and should exit with
-# success only for refs for which you want to run CI.
-
-case "$1" in
-# allow one-off tests by pushing to "for-ci" or "for-ci/mybranch"
-refs/heads/for-ci*) true ;;
-# always build your integration branch
-refs/heads/my-integration-branch) true ;;
-# don't build any other branches or tags
-*) false ;;
-esac