`HighsSolution::hasUndefined()` is now const #3914

Job	Run time
debug (ubuntu-latest)	3m 57s
debug_all_tests (ubuntu-latest)	4m 3s
release (ubuntu-latest)	3m 36s
release_all_tests (ubuntu-latest)	3m 31s
debug64 (ubuntu-latest)	3m 55s
debug64_all_tests (ubuntu-latest)	4m 7s
Release64 (ubuntu-latest)	3m 33s
Release64_all_tests (ubuntu-latest)	3m 29s
	30m 11s

Provide feedback