refactor: only running dependabot PR pipelines sequentially

Author: mfranzke

.github/workflows/default.yml

@@ -8,9 +8,19 @@ on:
     branches:
       - "main"
 
+# We'd like to run the pipeline for dependabot PRs sequentially, and all other PRs in parallel, but still only one action run for each PR.
 concurrency:
-  group: ${{ github.workflow }}-${{ github.ref }}
-  cancel-in-progress: ${{ github.ref != 'refs/heads/main' }}
+  group: >-
+    ${{
+      github.actor == 'dependabot[bot]' &&
+      'dependabot' ||
+      format('{0}-{1}', github.workflow, github.ref)
+    }}
+  cancel-in-progress: >-
+    ${{
+      github.actor != 'dependabot[bot]' &&
+      github.ref != 'refs/heads/main'
+    }}
 
 jobs:
   init: