Add OpenSSL::Digest.digests to get a list of available digests #973

Job	Run time
openssl-1.0.2u	2m 21s
openssl-1.1.0l	1m 36s
openssl-1.1.1w	1m 40s
openssl-3.0.13	2m 56s
openssl-3.1.5	3m 4s
openssl-3.2.1	3m 26s
libressl-3.1.5	2m 7s
libressl-3.2.7	2m 14s
libressl-3.3.6	2m 17s
libressl-3.4.3	2m 12s
libressl-3.5.3	2m 20s
libressl-3.6.3	2m 12s
libressl-3.7.3	2m 22s
libressl-3.8.2	2m 10s
openssl-3.0.13 fips	2m 41s
openssl-3.1.5 fips	2m 47s
openssl-3.2.1 fips	3m 7s
openssl-head	3m 22s
openssl-head fips	3m 19s
ruby-versions / Generate Ruby versions	1s
ubuntu-22.04 2.7	1m 0s
ubuntu-22.04 3.0	51s
ubuntu-22.04 3.1	1m 1s
ubuntu-22.04 3.2	1m 1s
ubuntu-22.04 3.3	57s
ubuntu-22.04 head	56s
ubuntu-22.04 truffleruby	1m 31s
ubuntu-22.04 truffleruby-head	1m 31s
ubuntu-20.04 2.7	57s
ubuntu-20.04 3.0	52s
ubuntu-20.04 3.1	51s
ubuntu-20.04 3.2	51s
ubuntu-20.04 3.3	48s
ubuntu-20.04 head	50s
ubuntu-20.04 truffleruby-head	1m 24s
macos-latest 2.7	1m 41s
macos-latest 3.0	1m 31s
macos-latest 3.1	1m 11s
macos-latest 3.2	1m 19s
macos-latest 3.3	1m 6s
macos-latest head	1m 1s
macos-latest truffleruby-head	1m 40s
windows-latest 2.7	5m 40s
windows-latest 3.0	4m 21s
windows-latest 3.1	4m 6s
windows-latest 3.2	4m 43s
windows-latest 3.3	4m 43s
windows-latest ucrt	3m 39s
windows-latest mswin	2m 39s
	1h 42m 55s

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