Merge #3021

3021: Fix CI against bundler's master r=deivid-rodriguez a=deivid-rodriguez

# Description:

Current run seems to be failing. I'm not sure exactly why. Nothing has changed in `bundler` in the last few days, so maybe it's order dependent, and now I tried this order way of doing it and it passed... 🤷‍♂️ 

# Tasks:

- [x] Describe the problem / feature
- [ ] Write tests
- [x] Write code to solve the problem
- [ ] Get code review from coworkers / friends

I will abide by the [code of conduct](https://github.com/rubygems/rubygems/blob/master/CODE_OF_CONDUCT.md).


Co-authored-by: David Rodríguez <deivid.rodriguez@riseup.net>

lib/rubygems/core_ext/kernel_warn.rb

@@ -6,12 +6,10 @@
   module Kernel
     path = "#{__dir__}/" # Frames to be skipped start with this path.
 
-    # Suppress "method redefined" warning
-    original_warn = instance_method(:warn)
-    Module.new {define_method(:warn, original_warn)}
-
     original_warn = method(:warn)
 
+    remove_method :warn
+
     class << self
 
       remove_method :warn