gh/action: add missing locales for tests/fmt/non-space.sh

Author: sylvestre

.github/workflows/GnuTests.yml

@@ -166,6 +166,7 @@ jobs:
         sudo locale-gen --keep-existing sv_SE
         sudo locale-gen --keep-existing sv_SE.UTF-8
         sudo locale-gen --keep-existing en_US
+        sudo locale-gen --keep-existing en_US.UTF-8
         sudo locale-gen --keep-existing ru_RU.KOI8-R
 
         sudo update-locale