Autocorrection of heredocs is an error

[dduugg]

This is observed for both Minitest/AssertEmpty and Minitest/AssertIncludes.
For example:

-      assert(task.result.include?(line), <<~EOF
-        Expected to find "#{line}" but couldn't.
-        Actual output was:
-          #{task.result.join("\n  ")}
-      EOF
-      )
+      assert_includes(task.result, line, <<~EOF)

I'm using rubocop 0.74.0 and rubocop-minitest 0.5.0