Allow SP certificates to be OpenSSL::X509::Certificate #390

Job	Run time
rubocop	9s
Unit test (ubuntu-20.04, 3)	1m 46s
Unit test (ubuntu-20.04, 3.1)	1m 48s
Unit test (ubuntu-20.04, 3.2)	1m 50s
Unit test (ubuntu-20.04, 3.3)	1m 52s
Unit test (ubuntu-20.04, jruby-9.4)	2m 28s
Unit test (ubuntu-20.04, truffleruby)	3m 45s
Unit test (macos-latest, 3)	1m 33s
Unit test (macos-latest, 3.1)	1m 41s
Unit test (macos-latest, 3.2)	1m 39s
Unit test (macos-latest, 3.3)	2m 4s
Unit test (macos-latest, jruby-9.4)	2m 0s
Unit test (macos-latest, truffleruby)	2m 36s
Unit test (windows-latest, 3)	3m 37s
Unit test (windows-latest, 3.1)	3m 4s
Unit test (windows-latest, 3.2)	3m 11s
Unit test (windows-latest, 3.3)	4m 35s
finish	5s
	39m 43s

Provide feedback