Update fsfe/reuse-action action to v6

Author: renovate[bot]

.github/workflows/reuse.yml

@@ -16,4 +16,4 @@ jobs:
     runs-on: ubuntu-24.04
     steps:
       - uses: actions/checkout@v6
-      - uses: fsfe/reuse-action@v5
+      - uses: fsfe/reuse-action@v6