Use concurrency for GitHub Actions workflow

This PR ensures that only the last execution per branch
always works, even when pushed multiple times in a row,
for example. The older one is canceled.

Refs:
https://docs.github.com/en/actions/using-jobs/using-concurrency
https://github.blog/changelog/2021-04-19-github-actions-limit-workflow-run-or-job-concurrency/

.github/workflows/codespell.yml

@@ -1,6 +1,9 @@
 name: CodeSpell
 on:
   - pull_request
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
 jobs:
   codespell:
     name: CodeSpell

.github/workflows/linting.yml

@@ -1,6 +1,9 @@
 name: Linting
 on:
   - pull_request
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
 jobs:
   yamllint:
     name: Yamllint

.github/workflows/main.yml

@@ -6,6 +6,10 @@ on:
     branches:
       - master
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   confirm_config_and_documentation:
     runs-on: ubuntu-latest