copyrights - fetch depth 50

.github/workflows/ci-main.yml

@@ -41,7 +41,7 @@ jobs:
   copyright: # check takes a bit longer and does not need to run in docker
     runs-on: ubuntu-latest
     steps:
-      - { uses: actions/checkout@v4, with: { fetch-depth: 0 } }
+      - { uses: actions/checkout@v4, with: { fetch-depth: 50 } }
 
       - name: Copyright check
         run: ./update_copyrights --output=