test/openssl/test_x509cert.rb: Prevent "unused variable" warning

(cherry picked from commit ruby/ruby@ab2bd3f)

Author: mame

test/openssl/test_x509cert.rb

@@ -316,7 +316,7 @@ def test_load_file_fullchain_garbage
     fullchain_path = Fixtures.file_path("pkey", "garbage.txt")
 
     assert_raise(OpenSSL::X509::CertificateError) do
-      certificates = OpenSSL::X509::Certificate.load_file(fullchain_path)
+      OpenSSL::X509::Certificate.load_file(fullchain_path)
     end
   end