make bn shareable when frozen #1189

Job	Run time
openssl-1.0.2u	2m 32s
openssl-1.1.0l	1m 31s
openssl-1.1.1w	1m 50s
ruby-versions / Generate Ruby versions	1s
openssl-3.0.15	3m 4s
openssl-3.1.7	3m 13s
openssl-3.2.3	3m 31s
openssl-3.3.2	3m 39s
openssl-master	3m 38s
libressl-3.1.5	2m 6s
libressl-3.2.7	2m 20s
libressl-3.3.6	2m 17s
libressl-3.4.3	2m 23s
libressl-3.5.3	2m 19s
libressl-3.6.3	2m 23s
libressl-3.7.3	2m 21s
libressl-3.8.4	2m 18s
libressl-3.9.2	2m 8s
openssl-3.0.15 with fips provider	2m 46s
openssl-3.1.7 with fips provider	2m 49s
openssl-3.2.3 with fips provider	3m 13s
openssl-3.3.2 with fips provider	3m 17s
openssl-master with fips provider	3m 21s
openssl-3.3.2 without legacy provider	3m 31s
ubuntu-22.04 2.7	33s
ubuntu-22.04 3.0	1m 0s
ubuntu-22.04 3.1	1m 4s
ubuntu-22.04 3.2	1m 4s
ubuntu-22.04 3.3	1m 3s
ubuntu-22.04 head	1m 0s
ubuntu-22.04 truffleruby	1m 36s
ubuntu-22.04 truffleruby-head	1m 46s
ubuntu-20.04 2.7	35s
ubuntu-20.04 3.0	1m 3s
ubuntu-20.04 3.1	1m 0s
ubuntu-20.04 3.2	1m 2s
ubuntu-20.04 3.3	58s
ubuntu-20.04 head	1m 3s
ubuntu-20.04 truffleruby	1m 36s
ubuntu-20.04 truffleruby-head	1m 50s
macos-latest 2.7	36s
macos-latest 3.0	41s
macos-latest 3.1	42s
macos-latest 3.2	39s
macos-latest 3.3	40s
macos-latest head	40s
macos-latest truffleruby	1m 11s
macos-latest truffleruby-head	1m 3s
windows-latest 2.7	3m 51s
windows-latest 3.0	5m 36s
windows-latest 3.1	5m 39s
windows-latest 3.2	4m 25s
windows-latest 3.3	5m 51s
windows-latest head	4m 15s
windows-latest ucrt	3m 45s
windows-latest mswin	3m 19s
	2h 3m 37s

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