Publish to PyPI when version tags are pushed.

Switch the publish workflow from GitHub Release events to tag pushes so
`git push origin vX.Y.Z` is enough to ship a new package.

Author: eddietejeda

.github/workflows/publish.yml

@@ -1,8 +1,16 @@
 name: Publish to PyPI
 
 on:
-  release:
-    types: [published]
+  push:
+    tags:
+      - 'v[0-9]*'
+
+concurrency:
+  group: pypi-publish-${{ github.ref_name }}
+  cancel-in-progress: false
+
+permissions:
+  contents: read
 
 jobs:
   build: