test/openssl/test_pkey_rsa: disable test_no_private_exp on OpenSSL 3.0

OpenSSL::PKey::RSA#set_key does not exist when built with OpenSSL 3.0,
so it is not possible to create an RSA object with incomplete state.

Author: rhenium

test/openssl/test_pkey_rsa.rb

@@ -11,7 +11,7 @@ def test_no_private_exp
     key.set_factors(rsa.p, rsa.q)
     assert_raise(OpenSSL::PKey::RSAError){ key.private_encrypt("foo") }
     assert_raise(OpenSSL::PKey::RSAError){ key.private_decrypt("foo") }
-  end
+  end if !openssl?(3, 0, 0) # Impossible state in OpenSSL 3.0
 
   def test_private
     # Generated by key size and public exponent