Warn to install ostruct if json couldn't load it #253

Job	Run time
ruby-versions / Generate Ruby versions	4s
ubuntu-20.04 2.3	57s
ubuntu-20.04 2.4	58s
ubuntu-20.04 2.5	56s
ubuntu-20.04 2.6	57s
ubuntu-20.04 2.7	57s
ubuntu-20.04 3.0	28s
ubuntu-20.04 3.1	39s
ubuntu-20.04 3.2	21s
ubuntu-20.04 3.3	23s
ubuntu-20.04 head	20s
ubuntu-20.04 jruby	1m 11s
ubuntu-20.04 jruby-head	1m 11s
ubuntu-22.04 2.3	1m 0s
ubuntu-22.04 2.4	56s
ubuntu-22.04 2.5	57s
ubuntu-22.04 2.6	57s
ubuntu-22.04 2.7	1m 4s
ubuntu-22.04 3.0	20s
ubuntu-22.04 3.1	25s
ubuntu-22.04 3.2	18s
ubuntu-22.04 3.3	24s
ubuntu-22.04 head	32s
ubuntu-22.04 jruby	1m 11s
ubuntu-22.04 jruby-head	1m 7s
macos-12 2.3	2m 26s
macos-12 2.4	2m 19s
macos-12 2.5	2m 10s
macos-12 2.6	2m 2s
macos-12 2.7	1m 49s
macos-12 3.0	23s
macos-12 3.1	26s
macos-12 3.2	34s
macos-12 3.3	28s
macos-12 head	26s
macos-12 jruby	2m 18s
macos-12 jruby-head	58s
macos-13 2.3	2m 23s
macos-13 2.4	2m 2s
macos-13 2.5	2m 31s
macos-13 2.6	2m 19s
macos-13 2.7	2m 30s
macos-13 3.0	27s
macos-13 3.1	25s
macos-13 3.2	25s
macos-13 3.3	29s
macos-13 head	27s
macos-13 jruby	1m 7s
macos-13 jruby-head	1m 7s
macos-14 2.6	1m 4s
macos-14 2.7	56s
macos-14 3.0	18s
macos-14 3.1	19s
macos-14 3.2	16s
macos-14 3.3	20s
macos-14 head	16s
macos-14 jruby	41s
macos-14 jruby-head	43s
windows-latest 2.3	1m 56s
windows-latest 2.4	3m 17s
windows-latest 2.5	4m 25s
windows-latest 2.6	4m 13s
windows-latest 2.7	2m 54s
windows-latest 3.0	1m 41s
windows-latest 3.1	1m 23s
windows-latest 3.2	2m 6s
windows-latest 3.3	2m 35s
windows-latest head	1m 47s
windows-latest mswin	2m 2s
ubuntu-latest jruby-9.1	1m 31s
ubuntu-latest jruby-9.2	1m 27s
ubuntu-latest jruby-9.3	1m 6s
ubuntu-latest jruby-9.4	1m 9s
	1h 29m 29s

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