feat: add concurrency to workflow

Allow only one workflow at that time.

If a second workflow is triggered, it will be put in pending state, and
only start once the first workflow finish.
If the workflow is triggered a third time while the first one is
running, the second workflow is canceled, and the third takes over the
pending state.

`github.head_ref` allows concurrent runs outside the main branch.

Fix opentofu#163.

.github/workflows/bump-and-publish-versions-prod.yml

@@ -5,6 +5,9 @@ on:
     - cron: '5 * * * *'
   workflow_dispatch:
 
+concurrency:
+  group: ${{ github.head_ref }}
+
 jobs:
   bump-versions:
     uses: opentofu/registry/.github/workflows/bump-versions.yml@main
@@ -17,4 +20,4 @@ jobs:
     uses: opentofu/registry/.github/workflows/generate-and-deploy.yml@main
     secrets: inherit
     with:
-      environment: "Production"
+      environment: "Production"