Fix test_pkey_ec.rb on FIPS. #871

Job	Run time
openssl-1.0.2u	3m 44s
openssl-1.1.0l	2m 15s
openssl-1.1.1v	2m 33s
openssl-3.0.10	4m 34s
ruby-versions / Generate Ruby versions	3s
openssl-3.1.2	4m 28s
libressl-3.1.5	3m 35s
libressl-3.2.7	3m 48s
libressl-3.3.6	3m 14s
libressl-3.4.3	3m 59s
libressl-3.5.3	4m 13s
libressl-3.6.3	3m 4s
libressl-3.7.3	3m 39s
libressl-3.8.0	3m 16s
openssl-3.0.10 fips	5m 51s
openssl-3.1.2 fips	5m 35s
openssl-head	6m 38s
openssl-head fips	5m 35s
ubuntu-22.04 2.7	1m 25s
ubuntu-22.04 3.0	1m 23s
ubuntu-22.04 3.1	1m 24s
ubuntu-22.04 3.2	1m 12s
ubuntu-22.04 head	1m 10s
ubuntu-22.04 truffleruby	1m 59s
ubuntu-22.04 truffleruby-head	2m 18s
ubuntu-20.04 2.7	1m 25s
ubuntu-20.04 3.0	1m 9s
ubuntu-20.04 3.1	1m 25s
ubuntu-20.04 3.2	1m 3s
ubuntu-20.04 head	1m 7s
ubuntu-20.04 truffleruby-head	1m 46s
macos-latest 2.7	2m 37s
macos-latest 3.0	1m 30s
macos-latest 3.1	1m 43s
macos-latest 3.2	1m 22s
macos-latest head	1m 34s
macos-latest truffleruby-head	4m 9s
windows-latest 2.7	7m 31s
windows-latest 3.0	5m 0s
windows-latest 3.1	9m 3s
windows-latest 3.2	10m 54s
windows-latest ucrt	6m 55s
windows-latest mswin	8m 26s
	2h 29m 34s

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