Do not install libimagequant

Author: radarhere

.github/workflows/test-mingw.yml

@@ -60,7 +60,6 @@ jobs:
               mingw-w64-x86_64-gcc \
               mingw-w64-x86_64-ghostscript \
               mingw-w64-x86_64-lcms2 \
-              mingw-w64-x86_64-libimagequant \
               mingw-w64-x86_64-libjpeg-turbo \
               mingw-w64-x86_64-libraqm \
               mingw-w64-x86_64-libtiff \