github/workflows: switch back to luajit for macos

Homebrew finally pulled the plug on lua 5.1*, and it is no more. So we
have to change to a different lua package and the only other choice is
luajit (no 5.2 in homebrew). We used to use luajit for the ci, but
649556b2b6 switched it to lua 5.1. As
explained there, luajit 2.0 was horribly bugged and not usuable for mpv
and the build had to do dumb hacks to work around it. I expected 5.1 to
last a bit longer than a couple of years, but luckily it seems like
luajit in homebrew now pulls a luajit 2.1 version (some rolling release
thing or however upstream works). The details don't really matter for
us since 2.1 does not have all the awful issues that 2.0 used to have.
So just switch to luajit again.

*: 57d73df3ba

.github/workflows/build.yml

@@ -108,7 +108,7 @@ jobs:
       - name: Install dependencies
         run: |
           brew update
-          brew install autoconf automake pkg-config libtool python freetype fribidi little-cms2 lua@5.1 libass ffmpeg meson libplacebo
+          brew install autoconf automake pkg-config libtool python freetype fribidi little-cms2 luajit libass ffmpeg meson libplacebo
 
       - name: Build with meson
         id: build