chore: switch to automated publishing workflow

.github/workflows/publish.yaml

@@ -0,0 +1,13 @@
+name: Publish to pub.dev
+
+on:
+  push:
+    tags:
+    - 'v[0-9]+.[0-9]+.[0-9]+*'
+
+# Publish using the reusable workflow from dart-lang.
+jobs:
+  publish:
+    permissions:
+      id-token: write # Required for authentication using OIDC
+    uses: dart-lang/setup-dart/.github/workflows/publish.yml@v1