CI mac: keep vulkan 1.3.262 temporarily

Install vulkan headers prior to updating homebrew tree.

the version 1.3.264 seem to be temporarily broken (see [1]), producing
error:

    /usr/local/include/vulkan/vulkan.hpp:15:10: fatal error: 'vulkan/vulkan_hpp_macros.hpp' file not found
    #include <vulkan/vulkan_hpp_macros.hpp>

[1]:
https://github.com/MartinPulec/UltraGrid/actions/runs/6184953701/job/16789584064

.github/scripts/macOS/prepare.sh

@@ -23,6 +23,7 @@ echo "PKG_CONFIG_PATH=/usr/local/lib/pkgconfig" >> "$GITHUB_ENV"
 echo "/usr/local/opt/qt/bin" >> "$GITHUB_PATH"
 echo "DYLIBBUNDLER_FLAGS=$DYLIBBUNDLER_FLAGS" >> "$GITHUB_ENV"
 
+brew install molten-vk vulkan-headers
 # TOREMOVE
 if [ "$(brew config | awk '/HOMEBREW_VERSION/{print $2}')" == 4.1.7 ]; then
         brew update
@@ -31,7 +32,6 @@ fi
 brew install autoconf automake libtool pkg-config
 brew install libsoxr speexdsp
 brew install ffmpeg portaudio sdl2 sdl2_mixer sdl2_ttf
-brew install molten-vk vulkan-headers
 brew install imagemagick libcaca libnatpmp jack opencv wolfssl
 brew install ossp-uuid # for cineform
 brew install qt@5