Add `rb_gc_guard!` macro with same behavior as `RB_GC_GUARD` (#221) #465

Job	Run time
oxi-test (ruby=2.7, os=ubuntu-latest)	1m 47s
oxi-test (ruby=3.2, os=ubuntu-latest)	1m 40s
oxi-test (ruby=ruby-head, os=ubuntu-latest)	1m 30s
oxi-test (ruby=2.7, os=windows-latest)	6m 30s
oxi-test (ruby=3.2, os=windows-latest)	10m 27s
oxi-test (ruby=ruby-head, os=windows-latest)	6m 51s
oxi-test (ruby=2.7, os=macos-latest)	3m 28s
oxi-test (ruby=3.2, os=macos-latest)	2m 4s
oxi-test (ruby=ruby-head, os=macos-latest)	2m 9s
magnus-0.5 (ruby=2.7, os=ubuntu-latest)	3m 10s
magnus-0.5 (ruby=3.2, os=ubuntu-latest)	2m 16s
magnus-0.5 (ruby=ruby-head, os=ubuntu-latest)	2m 30s
magnus-0.5 (ruby=2.7, os=windows-latest)	10m 41s
magnus-0.5 (ruby=3.2, os=windows-latest)	11m 49s
magnus-0.5 (ruby=2.7, os=macos-latest)	3m 23s
magnus-0.5 (ruby=3.2, os=macos-latest)	3m 26s
magnus-0.5 (ruby=ruby-head, os=macos-latest)	3m 20s
magnus-head (ruby=2.7, os=ubuntu-latest)	4m 38s
magnus-head (ruby=3.2, os=ubuntu-latest)	4m 4s
magnus-head (ruby=ruby-head, os=ubuntu-latest)	4m 3s
magnus-head (ruby=2.7, os=windows-latest)	10m 56s
magnus-head (ruby=3.2, os=windows-latest)	13m 59s
magnus-head (ruby=2.7, os=macos-latest)	4m 52s
magnus-head (ruby=3.2, os=macos-latest)	4m 54s
magnus-head (ruby=ruby-head, os=macos-latest)	4m 22s
	2h 8m 49s

Provide feedback