ci/mac: add homebrew libarchive pkg-config path to PKG_CONFIG_PATH

libarchive can't be linked globally because macOS already has an old
outdated version installed.

ci/build-macos.sh

@@ -12,7 +12,7 @@ if [[ -d "./build/${MPV_VARIANT}" ]] ; then
     rm -rf "./build/${MPV_VARIANT}"
 fi
 
-PKG_CONFIG_PATH="${FFMPEG_SYSROOT}/lib/pkgconfig/" CC="${CC}" CXX="${CXX}" \
+PKG_CONFIG_PATH="${FFMPEG_SYSROOT}/lib/pkgconfig/:$(brew --prefix libarchive)/lib/pkgconfig/" CC="${CC}" CXX="${CXX}" \
 meson setup build $common_args \
   -Dprefix="${MPV_INSTALL_PREFIX}" \
   -Dobjc_args="-Wno-error=deprecated -Wno-error=deprecated-declarations" \