ci: auto-trigger docker build on release tag push

docker-dispatch.yaml previously only fired on push to main and manual
workflow_dispatch, so tagging 1.11.0 did not build the release image.
This change adds matching of X.Y.Z tag.

.github/workflows/docker-dispatch.yaml

@@ -9,6 +9,7 @@ name: Trigger Docker build
 on:
   push:
     branches: [main]
+    tags: ['[0-9]+.[0-9]+.[0-9]+']
   workflow_dispatch:
 
 permissions: {}