[TASK] Set concurrency limits for the GH Action workflows (#1633)

https://docs.zizmor.sh/audits/#concurrency-limits

Part of #1628

Author: oliverklee

.github/workflows/ci.yml

@@ -13,6 +13,10 @@ name: CI
 permissions:
     contents: read
 
+concurrency:
+    group: ci-${{ github.event.pull_request.number || github.ref }}
+    cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
 jobs:
     php-lint:
         name: PHP Lint

.github/workflows/codecoverage.yml

@@ -11,6 +11,10 @@ name: Code coverage
 permissions:
     contents: read
 
+concurrency:
+    group: coverage-${{ github.event.pull_request.number || github.ref }}
+    cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
 jobs:
     code-coverage:
         name: Code coverage