Merge pull request #31069 from danott/resolve-minitest-deprecation-in-assert_no_changes

Resolve Minitest 6 deprecation in assert_no_changes

activesupport/lib/active_support/testing/assertions.rb

@@ -190,7 +190,12 @@ def assert_no_changes(expression, message = nil, &block)
 
         error = "#{expression.inspect} did change to #{after}"
         error = "#{message}.\n#{error}" if message
-        assert_equal before, after, error
+
+        if before.nil?
+          assert_nil after, error
+        else
+          assert_equal before, after, error
+        end
 
         retval
       end