Add test coverage for JSON.load with a Proc #40

Job	Run time
ruby-versions / Generate Ruby versions	3s
ubuntu-20.04 2.3	36s
ubuntu-20.04 2.4	35s
ubuntu-20.04 2.5	41s
ubuntu-20.04 2.6	41s
ubuntu-20.04 2.7	1m 4s
ubuntu-20.04 3.0	30s
ubuntu-20.04 3.1	32s
ubuntu-20.04 3.2	46s
ubuntu-20.04 3.3	29s
ubuntu-20.04 head	26s
ubuntu-20.04 jruby	48s
ubuntu-20.04 jruby-head	56s
ubuntu-22.04 2.3	38s
ubuntu-22.04 2.4	38s
ubuntu-22.04 2.5	1m 17s
ubuntu-22.04 2.6	39s
ubuntu-22.04 2.7	38s
ubuntu-22.04 3.0	26s
ubuntu-22.04 3.1	26s
ubuntu-22.04 3.2	32s
ubuntu-22.04 3.3	26s
ubuntu-22.04 head	21s
ubuntu-22.04 jruby	51s
ubuntu-22.04 jruby-head	48s
macos-12 2.3	1m 12s
macos-12 2.4	58s
macos-12 2.5	1m 1s
macos-12 2.6	1m 2s
macos-12 2.7	1m 8s
macos-12 3.0	28s
macos-12 3.1	28s
macos-12 3.2	28s
macos-12 3.3	37s
macos-12 head	27s
macos-12 jruby	44s
macos-12 jruby-head	42s
macos-13 2.3	1m 19s
macos-13 2.4	1m 49s
macos-13 2.5	1m 1s
macos-13 2.6	1m 14s
macos-13 2.7	1m 6s
macos-13 3.0	30s
macos-13 3.1	54s
macos-13 3.2	38s
macos-13 3.3	49s
macos-13 head	31s
macos-13 jruby	1m 19s
macos-13 jruby-head	54s
macos-14 2.6	50s
macos-14 2.7	32s
macos-14 3.0	18s
macos-14 3.1	24s
macos-14 3.2	23s
macos-14 3.3	19s
macos-14 head	17s
macos-14 jruby	35s
macos-14 jruby-head	28s
windows-latest 2.3	1m 11s
windows-latest 2.4	1m 45s
windows-latest 2.5	4m 6s
windows-latest 2.6	3m 21s
windows-latest 2.7	2m 29s
windows-latest 3.0	2m 34s
windows-latest 3.1	2m 16s
windows-latest 3.2	1m 52s
windows-latest 3.3	2m 39s
windows-latest head	1m 12s
windows-latest mswin	1m 52s
ubuntu-latest jruby-9.3	45s
ubuntu-latest jruby-9.4	43s
macos-latest truffleruby-head	29s
ubuntu-latest truffleruby-head	51s
	1h 9m 17s

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