Make clear source of environment.yml commit

Make it clear that the commit is made by a GitHub action by putting that
in the commit message title.

.github/workflows/conda-env.yml

@@ -32,6 +32,6 @@ jobs:
             git config --global user.name "${{ github.actor }}"
             git config --global user.email "${{ github.actor }}@users.noreply.github.com"
             git add environment.yml
-            git commit -m 'Update environment.yml'
+            git commit -m 'Update `environment.yml` via GitHub action'
             git push origin ${{ github.event.pull_request.head.ref }}
           fi