Testing minima is unstable

[Danack]

//TEST 275/284 [tests/287_Imagick_GetImageChannelRange_basic.phpt]
//========DIFF========
//001+ Unexpected green minima. Was expecting 8224 but have 8226
//========DONE========

This is an off by a tiny bit error.

It would need to be part of a test suite in ImageMagick before it can be safely tested on every version of Imagick