ci(goreleaser): use concurrency to only execute 1 job at a time (gn…

…olang#3557)

This will make it so that on master, there is only 1 job of
releaser-master executing at a time. There may be another pending one
(if, say, we merge two PRs back to back), and it will be put as
`pending`. It's cancelled if we merge a third PR while the second one is
still `pending`.

For more information:
https://docs.github.com/en/actions/writing-workflows/workflow-syntax-for-github-actions#concurrency

.github/workflows/releaser-master.yml

@@ -6,6 +6,9 @@ on:
       - master
   workflow_dispatch:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref || github.run_id }}
+
 permissions:
   contents: write # needed to write releases
   id-token: write # needed for keyless signing