Fix test_pkey_rsa.rb in FIPS. #1153

Job	Run time
openssl-1.0.2u	55s
openssl-1.1.0l	51s
openssl-1.1.1w	58s
openssl-3.0.14	57s
openssl-3.1.6	1m 0s
openssl-3.2.2	59s
openssl-3.3.1	1m 0s
openssl-master	3m 39s
libressl-3.1.5	59s
libressl-3.2.7	57s
libressl-3.3.6	58s
libressl-3.4.3	56s
libressl-3.5.3	1m 3s
libressl-3.6.3	1m 1s
libressl-3.7.3	56s
libressl-3.8.4	58s
libressl-3.9.2	55s
openssl-3.0.14 with fips provider	38s
openssl-3.1.6 with fips provider	42s
openssl-3.2.2 with fips provider	42s
openssl-3.3.1 with fips provider	38s
openssl-master with fips provider	3m 19s
openssl-3.3.1 without legacy provider	56s
ruby-versions / Generate Ruby versions	3s
ubuntu-22.04 2.7	1m 1s
ubuntu-22.04 3.0	57s
ubuntu-22.04 3.1	1m 3s
ubuntu-22.04 3.2	57s
ubuntu-22.04 3.3	58s
ubuntu-22.04 head	1m 4s
ubuntu-22.04 truffleruby	1m 36s
ubuntu-22.04 truffleruby-head	1m 44s
ubuntu-20.04 2.7	56s
ubuntu-20.04 3.0	54s
ubuntu-20.04 3.1	59s
ubuntu-20.04 3.2	58s
ubuntu-20.04 3.3	57s
ubuntu-20.04 head	57s
ubuntu-20.04 truffleruby	1m 37s
ubuntu-20.04 truffleruby-head	1m 37s
macos-latest 2.7	54s
macos-latest 3.0	46s
macos-latest 3.1	41s
macos-latest 3.2	38s
macos-latest 3.3	45s
macos-latest head	38s
macos-latest truffleruby	55s
macos-latest truffleruby-head	1m 19s
windows-latest 2.7	5m 59s
windows-latest 3.0	3m 49s
windows-latest 3.1	3m 51s
windows-latest 3.2	3m 59s
windows-latest 3.3	5m 16s
windows-latest head	4m 13s
windows-latest ucrt	3m 39s
windows-latest mswin	2m 39s
	1h 24m 16s

Provide feedback