ci: watchtower HTTP API now requires POST, not GET, on /v1/update

The maintained fork (ghcr.io/nicholas-fedor/watchtower) returns 405
on GET; only POST is accepted.

.gitea/workflows/docker.yaml

@@ -32,4 +32,4 @@ jobs:
         env:
           TOKEN: ${{ secrets.WATCHTOWER_TOKEN }}
         run: |
-          curl -X GET -H "Authorization: Bearer $TOKEN" http://192.168.1.118:3026/v1/update
+          curl -X POST -H "Authorization: Bearer $TOKEN" http://192.168.1.118:3026/v1/update