Skip concurrent CI builds (#4)

Author: tobiasraabe

{{cookiecutter.package_name}}/.github/workflows/main.yml

@@ -1,4 +1,10 @@
 name: Continuous Integration Workflow
+
+# Automatically cancel a previous run.
+concurrency:
+  group: ${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
 on:
   push:
     branches: