Use fixed fetch-depth for copyright linter

The old trick to get needed commits doesn't work anymore. The context in
gitea unlike on github doesn't carry the number of commits, therefore
just fetch a fixed depth of 100 which is to reason should be enough.

Signed-off-by: Ralph Sennhauser <ralph.sennhauser@gmail.com>

.gitea/workflows/lint.yml

@@ -50,6 +50,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          fetch-depth: 100
 
       - uses: actions/setup-python@v5
         with: