sync-upstream-branches: configure the workflow via vars.CONFIG

The grand idea to use GitGitGadget for projects other than Git is to
allow configuring it via a custom JSON that is stored as a repository
variable.

Let's do this.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

.github/workflows/sync-upstream-branches.yml

@@ -16,24 +16,18 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        spec:
-          - source-repo: j6t/git-gui
-            target-repo: gitgitgadget/git
-            target-ref-namespace: git-gui/
-          - source-repo: gitster/git
-            target-repo: gitgitgadget/git
-            source-ref-regex: "^refs/heads/(maint-\\d|[a-z][a-z]/)"
+        spec: ${{ fromJSON(vars.CONFIG).syncUpstreamBranches }}
 
     steps:
       - name: check which refs need to be synchronized
         uses: actions/github-script@v7
         id: check
         with:
           script: |
-            const sourceRepo = ${{ toJSON(matrix.spec.source-repo) }}
-            const sourceRefRegexp = ((p) => p ? new RegExp(p) : null)(${{ toJSON(matrix.spec.source-ref-regex) }})
-            const targetRepo = ${{ toJSON(matrix.spec.target-repo) }}
-            const targetRefNamespace = ${{ toJSON(matrix.spec.target-ref-namespace) }}
+            const sourceRepo = ${{ toJSON(matrix.spec.sourceRepo) }}
+            const sourceRefRegexp = ((p) => p ? new RegExp(p) : null)(${{ toJSON(matrix.spec.sourceRefRegex) }})
+            const targetRepo = ${{ toJSON(matrix.spec.targetRepo) }}
+            const targetRefNamespace = ${{ toJSON(matrix.spec.targetRefNamespace) }}
 
             const [targetRepoOwner, targetRepoName] = targetRepo.split('/')
             core.setOutput('target-repo-owner', targetRepoOwner)