feat(workflows): add runner input, timeouts and release concurrency

The release, release-cgo and autoupdate workflows must run on a runner
the caller chooses. Each workflow now takes a runner input. It accepts
a label or a JSON object that selects a runner group.

The workflow uses inputs.runner first. It then uses the
SHARED_ACTIONS_RUNNER variable and falls back to ubuntu-latest. Callers
that set nothing keep the old behaviour.

Every job now has a timeout. Release and autoupdate runs use a
concurrency group that never cancels a running job.

.github/workflows/go-autoupdate.yaml

@@ -19,11 +19,22 @@ on:
         type: boolean
         default: false
 
+      runner:
+        description: "Runner label, or JSON object such as {\"group\":\"ci\",\"labels\":[\"linux\"]} to select a runner group. Falls back to vars.SHARED_ACTIONS_RUNNER, then ubuntu-latest."
+        required: false
+        type: string
+        default: ""
+
+concurrency:
+  group: autoupdate-${{ github.repository }}-${{ github.ref }}
+  cancel-in-progress: false
+
 jobs:
   autoupdate:
     name: Update dependencies and test
-    runs-on: ubuntu-latest
+    runs-on: ${{ fromJSON(startsWith(inputs.runner || vars.SHARED_ACTIONS_RUNNER || 'ubuntu-latest', '{') && inputs.runner || vars.SHARED_ACTIONS_RUNNER || 'ubuntu-latest' || toJSON(inputs.runner || vars.SHARED_ACTIONS_RUNNER || 'ubuntu-latest')) }}
 
+    timeout-minutes: 30
     steps:
       - name: Checkout
         uses: actions/checkout@v6