[rubygems/rubygems] Ignore GEMRC variable for test suite. It affects with some test case.

https://github.com/rubygems/rubygems/commit/4a0ca2583a

lib/rubygems/test_case.rb

@@ -246,6 +246,7 @@ class Gem::TestCase < (defined?(Minitest::Test) ? Minitest::Test : MiniTest::Uni
     @orig_env = ENV.to_hash
 
     ENV['GEM_VENDOR'] = nil
+    ENV['GEMRC'] = nil
     ENV['SOURCE_DATE_EPOCH'] = nil
 
     @current_dir = Dir.pwd