Only publish to Test PyPI for tags

Author: hugovk

.github/workflows/publish.yml

@@ -1,6 +1,6 @@
 # This workflow is triggered two ways:
 #
-# 1. When a commit is made, the workflow will upload the package to
+# 1. When a tag is created, the workflow will upload the package to
 #    test.pypi.org.
 # 2. When a release is made, the workflow will upload the package to pypi.org.
 #
@@ -34,13 +34,13 @@ jobs:
 
       - uses: hynek/build-and-inspect-python-package@fe0a0fb1925ca263d076ca4f2c13e93a6e92a33e # v2.17.0
 
-  # Publish to Test PyPI on every commit on main.
+  # Publish to Test PyPI for every tag.
   release-test-pypi:
     name: Publish in-dev package to test.pypi.org
     if: |
       github.repository_owner == 'python'
       && github.event_name == 'push'
-      && github.ref == 'refs/heads/main'
+      && startsWith(github.ref, 'refs/tags/')
     runs-on: ubuntu-latest
     needs: build-package