test fallback to v5 for gpg action

.gitea/workflows/release-nightly.yml

@@ -17,7 +17,7 @@ jobs:
           go-version-file: "go.mod"
       - name: import gpg
         id: import_gpg
-        uses: crazy-max/ghaction-import-gpg@v6
+        uses: crazy-max/ghaction-import-gpg@v5
         with:
           gpg_private_key: ${{ secrets.GPGSIGN_KEY }}
           passphrase: ${{ secrets.GPGSIGN_PASSPHRASE }}