test/openssl/test_pkey.rb: allow failures in test_s_generate_parameters

The root cause has been fixed by OpenSSL 3.0.6, but Ubuntu 22.04's
OpenSSL package has not backported the patch yet.

Reference: #492

Author: rhenium

test/openssl/test_pkey.rb

@@ -47,6 +47,11 @@ def test_s_generate_parameters
         raise "exit!" if cb_called.size == 3
       }
     }
+    if !cb_called && openssl?(3, 0, 0) && !openssl?(3, 0, 6)
+      # Errors in BN_GENCB were not properly handled. This special pend is to
+      # suppress failures on Ubuntu 22.04, which uses OpenSSL 3.0.2.
+      pend "unstable test on OpenSSL 3.0.[0-5]"
+    end
     assert_not_empty cb_called
   end