Release job version verification checks for an exact match

The step in the release process that checks whether a release number has
already been used, we are failing while trying to ship v2.2.2 because
v2.2.2rc1 already exists. We need to check for an exact match rather than
doing a simple grep match.

Use `git rev-parse` to do an exact match check for whether a git tag
already exists.

.github/workflows/publish-to-pypi.yaml

@@ -65,8 +65,9 @@ jobs:
 
       - name: Verify unique release number
         run: |
-          if git tag -l | grep -q ${{ steps.bump.outputs.VERSION_TAG }}; then
-            echo "Tag ${{ steps.bump.outputs.VERSION_TAG }} already exists, aborting"
+          TAG_NAME=${{ steps.bump.outputs.VERSION_TAG }}
+          if git rev-parse -q --verify "refs/tags/$TAG_NAME" >/dev/null; then
+            echo "Tag $TAG_NAME already exists."
             exit 1
           fi