Fix test_pkey_rsa.rb in FIPS. #1158

Job	Run time
openssl-1.0.2u	52s
openssl-1.1.0l	54s
openssl-1.1.1w	54s
openssl-3.0.14	57s
openssl-3.1.6	56s
openssl-3.2.2	55s
openssl-3.3.1	55s
openssl-master	3m 54s
libressl-3.1.5	52s
libressl-3.2.7	59s
libressl-3.3.6	58s
libressl-3.4.3	1m 2s
libressl-3.5.3	1m 0s
libressl-3.6.3	1m 5s
libressl-3.7.3	55s
libressl-3.8.4	56s
libressl-3.9.2	1m 2s
openssl-3.0.14 with fips provider	37s
openssl-3.1.6 with fips provider	38s
openssl-3.2.2 with fips provider	39s
openssl-3.3.1 with fips provider	44s
openssl-master with fips provider	3m 26s
openssl-3.3.1 without legacy provider	56s
ruby-versions / Generate Ruby versions	4s
ubuntu-22.04 2.7	1m 2s
ubuntu-22.04 3.0	51s
ubuntu-22.04 3.1	58s
ubuntu-22.04 3.2	1m 1s
ubuntu-22.04 3.3	57s
ubuntu-22.04 head	1m 3s
ubuntu-22.04 truffleruby	1m 36s
ubuntu-22.04 truffleruby-head	1m 35s
ubuntu-20.04 2.7	56s
ubuntu-20.04 3.0	57s
ubuntu-20.04 3.1	56s
ubuntu-20.04 3.2	1m 1s
ubuntu-20.04 3.3	1m 0s
ubuntu-20.04 head	56s
ubuntu-20.04 truffleruby	1m 34s
ubuntu-20.04 truffleruby-head	1m 34s
macos-latest 2.7	54s
macos-latest 3.0	37s
macos-latest 3.1	51s
macos-latest 3.2	42s
macos-latest 3.3	39s
macos-latest head	41s
macos-latest truffleruby	1m 33s
macos-latest truffleruby-head	1m 13s
windows-latest 2.7	5m 21s
windows-latest 3.0	4m 11s
windows-latest 3.1	4m 22s
windows-latest 3.2	4m 27s
windows-latest 3.3	5m 22s
windows-latest head	3m 55s
windows-latest ucrt	3m 52s
windows-latest mswin	2m 46s
	1h 25m 33s

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