make bn shareable when frozen #1229

Job	Run time
openssl-1.0.2u	50s
openssl-1.1.0l	56s
openssl-1.1.1w	53s
ruby-versions / Generate Ruby versions	7s
openssl-3.0.15	1m 6s
openssl-3.1.7	59s
openssl-3.2.3	1m 2s
openssl-3.3.2	1m 1s
openssl-3.4.0	57s
openssl-master	3m 40s
libressl-3.1.5	53s
libressl-3.2.7	1m 4s
libressl-3.3.6	59s
libressl-3.4.3	1m 1s
libressl-3.5.3	1m 7s
libressl-3.6.3	1m 2s
libressl-3.7.3	54s
libressl-3.8.4	56s
libressl-3.9.2	57s
libressl-4.0.0	1m 0s
openssl-3.0.15 with fips provider	45s
openssl-3.1.7 with fips provider	38s
openssl-3.2.3 with fips provider	39s
openssl-3.3.2 with fips provider	40s
openssl-3.4.0 with fips provider	40s
openssl-master with fips provider	3m 24s
openssl-3.4.0 without legacy provider	1m 1s
ubuntu-22.04 2.7	1m 3s
ubuntu-22.04 3.0	56s
ubuntu-22.04 3.1	55s
ubuntu-22.04 3.2	58s
ubuntu-22.04 3.3	57s
ubuntu-22.04 head	59s
ubuntu-22.04 truffleruby	1m 35s
ubuntu-22.04 truffleruby-head	1m 44s
ubuntu-20.04 2.7	1m 2s
ubuntu-20.04 3.0	56s
ubuntu-20.04 3.1	54s
ubuntu-20.04 3.2	57s
ubuntu-20.04 3.3	57s
ubuntu-20.04 head	55s
ubuntu-20.04 truffleruby	1m 28s
ubuntu-20.04 truffleruby-head	1m 40s
macos-latest 2.7	1m 20s
macos-latest 3.0	37s
macos-latest 3.1	43s
macos-latest 3.2	43s
macos-latest 3.3	42s
macos-latest head	55s
macos-latest truffleruby	1m 4s
macos-latest truffleruby-head	1m 42s
windows-latest 2.7	6m 21s
windows-latest 3.0	4m 19s
windows-latest 3.1	4m 11s
windows-latest 3.2	4m 6s
windows-latest 3.3	5m 47s
windows-latest head	4m 5s
windows-latest ucrt	4m 32s
windows-latest mswin	3m 19s
	1h 31m 33s

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