refactor(dependabot): only run one concurrent pipeline

Author: mfranzke

.github/workflows/default.yml

@@ -7,9 +7,19 @@ on:
     branches: [main]
   workflow_dispatch:
 
+# 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: true
+  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:
   # Stage 1: Parallel analysis jobs (no build required)