[ruby/openssl] pkey/ec: fix exception class in OpenSSL::PKey::EC.new

Fix a copy-and-paste error introduced in commit ruby/openssl@74f6c6175688 (pkey:
allocate EVP_PKEY on #initialize, 2021-04-12).

It should raise OpenSSL::PKey::ECError instead of
OpenSSL::PKey::DSAError.

ruby/openssl@b1f6a04abf

Author: rhenium

ext/openssl/ossl_pkey_ec.c

@@ -174,7 +174,7 @@ static VALUE ossl_ec_key_initialize(int argc, VALUE *argv, VALUE self)
     type = EVP_PKEY_base_id(pkey);
     if (type != EVP_PKEY_EC) {
         EVP_PKEY_free(pkey);
-        rb_raise(eDSAError, "incorrect pkey type: %s", OBJ_nid2sn(type));
+        rb_raise(eECError, "incorrect pkey type: %s", OBJ_nid2sn(type));
     }
     RTYPEDDATA_DATA(self) = pkey;
     return self;