Ensure gettext is available.

Author: freakboy3742

.github/workflows/ci.yml

@@ -25,7 +25,7 @@ jobs:
           pip install --upgrade setuptools wheel
           pip install -r requirements.txt
           lektor plugins reinstall
-          brew install msgfmt
+          brew install gettext
       - name: Clean
         run : |
           lektor clean -O output --yes