go to bug id or search bugs for
ImageMagick introduced a new colorspace constant in 6.9.9-28:
RGBColorspace, /* Linear RGB colorspace */
GRAYColorspace, /* greyscale (linear) image (faked 1 channel) */
In 6.9.9-30 this was changed to LinearGRAYColorspace.
Please incorporate them in pecl-imagick. Related to #75802 which mentions sGRAY but misses the later change.
Sorry for not including a patch. I don't know how to check MagickLibVersion for those particular versions.
Add a Patch
Add a Pull Request
This was added a while ago.