ci: use manual clone to work around Woodpecker OAuth issue

.woodpecker.yaml

@@ -5,7 +5,17 @@ when:
   - event: tag
     ref: "refs/tags/v*"
 
+skip_clone: true
+
 steps:
+  - name: clone
+    image: alpine/git
+    environment:
+      CLONE_TOKEN:
+        from_secret: registry_token
+    commands:
+      - git clone --depth 1 --branch $CI_COMMIT_TAG https://oleks:$CLONE_TOKEN@git.oleks.space/oleks/alertmanager-gotify-bridge.git .
+
   - name: build-and-push
     image: git.oleks.space/oleks/nix-ci:latest
     environment: