[rb] stop running flaky file upload tests on GitHub in Safari

No obvious race condition to wait for on the client side

rb/spec/integration/selenium/webdriver/remote/element_spec.rb

@@ -21,7 +21,7 @@
 
 module Selenium
   module WebDriver
-    describe Element, exclusive: {driver: :remote} do
+    describe Element, exclusive: {driver: :remote}, flaky: {browser: :safari, ci: :github} do
       before do
         driver.file_detector = ->(filename) { File.join(__dir__, filename) }
       end