Only run CI workflow once on pushes when there is a PR open.

Author: alfredeen

.github/workflows/ci.yaml

@@ -6,6 +6,7 @@ on:
     paths-ignore:
       - '**.md'
   pull_request:
+    types: [opened, reopened]
     branches: [ "*" ]
     paths-ignore:
       - '**.md'

README.md

@@ -22,6 +22,7 @@ git rebase origin/main
 Verify that the code adheres to the style guidelines and code analysis rules:
 ```bash
 flake8 .
+isort .
 black . --check
 hadolint Dockerfile
 ```