test

Don't call `rb_str_set_len` while released the GVL. #203

Job	Run time
ruby-versions / Generate Ruby versions	2s
build (2.5 / ubuntu-latest)	22s
build (2.5 / windows-latest)	3m 50s
build (2.6 / ubuntu-latest)	25s
build (2.6 / macos-latest)	34s
build (2.6 / windows-latest)	3m 0s
build (2.7 / ubuntu-latest)	23s
build (2.7 / macos-latest)	32s
build (2.7 / windows-latest)	3m 12s
build (3.0 / ubuntu-latest)	10s
build (3.0 / macos-latest)	15s
build (3.0 / windows-latest)	1m 27s
build (3.1 / ubuntu-latest)	13s
build (3.1 / macos-latest)	16s
build (3.1 / windows-latest)	1m 41s
build (3.2 / ubuntu-latest)	10s
build (3.2 / macos-latest)	15s
build (3.2 / windows-latest)	1m 51s
build (3.3 / ubuntu-latest)	10s
build (3.3 / macos-latest)	15s
build (3.3 / windows-latest)	1m 27s
build (head / ubuntu-latest)	9s
build (head / macos-latest)	17s
build (truffleruby-head / ubuntu-latest)	26s
build (truffleruby-head / macos-latest)	24s
build (mswin / windows-latest)	1m 39s
build (mingw / windows-latest)	57s
	24m 22s

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