ci/mac: install ffmpeg-full with homebrew when available

homebrew slimmed down their ffmpeg formula and stripping it off some
essential functionality.
Homebrew/homebrew-core#261303

use ffmpeg-full instead. this is keg only formula and not automatically
symlinked system wide. make sure ffmpeg is not installed in parallel and
install ffmpeg-full system wide.

Author: Akemi

.github/workflows/build.yml

@@ -295,9 +295,11 @@ jobs:
           else
             brew update
           fi
+          if brew list ffmpeg &> /dev/null; then brew unlink ffmpeg; fi
           brew install -q autoconf automake pkgconf libtool python freetype fribidi little-cms2 \
-            luajit libass ffmpeg meson rust uchardet mujs libplacebo molten-vk vulkan-loader vulkan-headers \
+            luajit libass ffmpeg-full meson rust uchardet mujs libplacebo molten-vk vulkan-loader vulkan-headers \
             libarchive libbluray libcaca libcdio-paranoia libdvdnav rubberband zimg
+          brew link ffmpeg-full
 
       - name: Build with meson
         id: build