fix MacOS build pipeline

libintl.h needs special magic to be found

.github/workflows/build_macos.yml

@@ -25,6 +25,8 @@ jobs:
     - name: Install dependencies
       run: |
         brew install sdl2
+        # gettext is a keg-only install so the headers are missing by default
+        brew unlink gettext && brew link gettext
     - name: Build and test
       env:
         CC: ${{ matrix.compiler }}