make bn shareable when frozen #1214

Job	Run time
openssl-1.0.2u	49s
openssl-1.1.0l	50s
openssl-1.1.1w	1m 1s
openssl-3.0.15	1m 2s
openssl-3.1.7	1m 2s
openssl-3.2.3	59s
openssl-3.3.2	57s
openssl-3.4.0	1m 2s
openssl-master	3m 43s
libressl-3.1.5	1m 1s
libressl-3.2.7	58s
libressl-3.3.6	59s
libressl-3.4.3	59s
libressl-3.5.3	1m 0s
libressl-3.6.3	1m 5s
libressl-3.7.3	59s
libressl-3.8.4	1m 3s
libressl-3.9.2	1m 3s
libressl-4.0.0	57s
openssl-3.0.15 with fips provider	39s
openssl-3.1.7 with fips provider	43s
openssl-3.2.3 with fips provider	43s
openssl-3.3.2 with fips provider	47s
openssl-3.4.0 with fips provider	44s
openssl-master with fips provider	3m 22s
openssl-3.4.0 without legacy provider	1m 13s
ruby-versions / Generate Ruby versions	3s
ubuntu-22.04 2.7	1m 0s
ubuntu-22.04 3.0	57s
ubuntu-22.04 3.1	1m 3s
ubuntu-22.04 3.2	1m 3s
ubuntu-22.04 3.3	59s
ubuntu-22.04 head	1m 4s
ubuntu-22.04 truffleruby	1m 30s
ubuntu-22.04 truffleruby-head	1m 42s
ubuntu-20.04 2.7	1m 10s
ubuntu-20.04 3.0	57s
ubuntu-20.04 3.1	56s
ubuntu-20.04 3.2	57s
ubuntu-20.04 3.3	53s
ubuntu-20.04 head	55s
ubuntu-20.04 truffleruby	1m 33s
ubuntu-20.04 truffleruby-head	1m 44s
macos-latest 2.7	1m 2s
macos-latest 3.0	38s
macos-latest 3.1	40s
macos-latest 3.2	50s
macos-latest 3.3	48s
macos-latest head	53s
macos-latest truffleruby	1m 28s
macos-latest truffleruby-head	1m 12s
windows-latest 2.7	4m 30s
windows-latest 3.0	3m 34s
windows-latest 3.1	3m 41s
windows-latest 3.2	4m 25s
windows-latest 3.3	4m 17s
windows-latest head	3m 53s
windows-latest ucrt	4m 10s
windows-latest mswin	2m 58s
	1h 27m 5s

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