ci: restrict shaderc version to fix build errors

KhronosGroup/glslang#3787 was fixed already
but shaderc uses pinned revisions, so let's just downgrade.

ci/build-mingw64.sh

@@ -164,6 +164,7 @@ _ffmpeg_mark=lib/libavcodec.dll.a
 _shaderc () {
     if [ ! -d shaderc ]; then
         $gitclone https://github.com/google/shaderc.git
+        (cd shaderc && git fetch --tags && git checkout v2024.3)
         (cd shaderc && ./utils/git-sync-deps)
     fi
     builddir shaderc

ci/build-win32.ps1

@@ -9,6 +9,7 @@ if (-not (Test-Path $subprojects)) {
 # Wrap shaderc to run git-sync-deps and patch unsupported generator expression
 if (-not (Test-Path "$subprojects/shaderc_cmake")) {
     git clone https://github.com/google/shaderc --depth 1 $subprojects/shaderc_cmake
+    git -C $subprojects/shaderc_cmake checkout v2024.3
     Set-Content -Path "$subprojects/shaderc_cmake/p.diff" -Value @'
 diff --git a/third_party/CMakeLists.txt b/third_party/CMakeLists.txt
 index d44f62a..54d4719 100644