Use RSTRING_END #757

Job	Run time
Ruby memcheck	2m 0s
ruby-versions / Generate Ruby versions	2s
ubuntu-22.04 2.7	57s
ubuntu-22.04 3.0	30s
ubuntu-22.04 3.1	33s
ubuntu-22.04 3.2	37s
ubuntu-22.04 3.3	30s
ubuntu-22.04 3.4	31s
ubuntu-22.04 head	1m 22s
ubuntu-22.04 jruby	1m 13s
ubuntu-22.04 jruby-head	1m 5s
macos-13 2.7	1m 55s
macos-13 3.0	54s
macos-13 3.1	55s
macos-13 3.2	38s
macos-13 3.3	41s
macos-13 3.4	36s
macos-13 head	29s
macos-13 jruby	2m 19s
macos-13 jruby-head	1m 35s
macos-14 2.7	58s
macos-14 3.0	24s
macos-14 3.1	30s
macos-14 3.2	19s
macos-14 3.3	27s
macos-14 3.4	24s
macos-14 head	21s
macos-14 jruby	44s
macos-14 jruby-head	40s
windows-latest 2.7	4m 54s
windows-latest 3.0	2m 5s
windows-latest 3.1	3m 12s
windows-latest 3.2	2m 19s
windows-latest 3.3	4m 27s
windows-latest 3.4	4m 11s
windows-latest head	1m 25s
windows-latest mswin	1m 29s
ubuntu-latest jruby-9.4	1m 3s
macos-latest truffleruby-head	47s
ubuntu-latest truffleruby-head	2m 3s
	52m 4s

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