Change i18n unused strings check to only check English strings (#39347)

.github/workflows/check-i18n.yml

@@ -39,7 +39,7 @@ jobs:
         run: bin/i18n-tasks check-normalized
 
       - name: Check for unused strings
-        run: bin/i18n-tasks unused
+        run: bin/i18n-tasks unused -l en
 
       - name: Check for missing strings in English YML
         run: |