Add required github deployment environment for publishing (#3544)

Pass environment config to the publish action to harden our releases.

Upon approval I will also update the publish settings on pub to require this environment.

(see https://dart.dev/tools/pub/automated-publishing#hardening-security-with-github-deployment-environments)

Author: jakemac53

.github/workflows/publish.yaml

@@ -14,4 +14,6 @@ jobs:
     if: ${{ github.repository_owner == 'dart-lang' }}
     uses: dart-lang/ecosystem/.github/workflows/publish.yaml@main
     with:
+      # Protected github deployment environment, requires approval to publish.
+      environment: pub.dev
       sdk: dev