build-matplotlib: specify files path in publish-wheels

Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>

Author: threexc

.github/workflows/build-matplotlib.yml

@@ -187,3 +187,4 @@ jobs:
           gitlab-token: ${{ secrets.GITLAB_DEPLOY_TOKEN }}
           gitlab-project-id: ${{ vars.GITLAB_PROJECT_ID }}
           gh-token: ${{ secrets.GITHUB_TOKEN }}
+          files: 'wheelhouse/*.whl'