Exclude Ruby 2.5 on macOS from CI #99

Job	Run time
ruby-versions / Generate Ruby versions	2s
test (2.5, ubuntu-latest)	40s
test (2.5, windows-latest)	4m 13s
test (2.6, ubuntu-latest)	42s
test (2.6, macos-latest)	50s
test (2.6, windows-latest)	3m 25s
test (2.7, ubuntu-latest)	41s
test (2.7, macos-latest)	43s
test (2.7, windows-latest)	3m 9s
test (3.0, ubuntu-latest)	17s
test (3.0, macos-latest)	16s
test (3.0, windows-latest)	1m 36s
test (3.1, ubuntu-latest)	22s
test (3.1, macos-latest)	16s
test (3.1, windows-latest)	1m 49s
test (3.2, ubuntu-latest)	21s
test (3.2, macos-latest)	15s
test (3.2, windows-latest)	1m 43s
test (3.3, ubuntu-latest)	19s
test (3.3, macos-latest)	15s
test (3.3, windows-latest)	2m 59s
test (head, ubuntu-latest)	19s
test (head, macos-latest)	15s
test (head, windows-latest)	1m 54s
test (jruby, ubuntu-latest)	1m 13s
test (jruby, macos-latest)	57s
test (jruby, windows-latest)	2m 17s
test (jruby-head, ubuntu-latest)	1m 15s
test (jruby-head, macos-latest)	1m 16s
test (jruby-head, windows-latest)	2m 18s
test (windows-latest, ucrt)	1m 25s
test (windows-latest, mingw)	1m 36s
test (windows-latest, mswin)	2m 32s
	42m 10s

Provide feedback