GHA: Install lua via homebrew on OSX

Author: Flamefire

.github/workflows/unit-tests.yml

@@ -162,7 +162,7 @@ jobs:
       - name: Install system packages
         run: |
           if [[ "${{runner.os}}" =~ macOS ]]; then
-            brew install cmake boost sdl2 sdl2_mixer gettext miniupnpc libiconv
+            brew install cmake boost sdl2 sdl2_mixer gettext miniupnpc libiconv lua
             echo /usr/local/opt/gettext/bin >> $GITHUB_PATH
             echo "Available Boost installs: $(ls /usr/local/Cellar/boost/)"
             # Use the latest (last folder)