Disable new BinaryOperatorWithIdenticalOperands lint..

- It was just added in 0.89.0
- It finds errors in simple math operations, has many errors reported,
such as:
  - rubocop/rubocop#8482
  - rubocop/rubocop#8478

It looks like the next version of rubocop may loosen it a bit, but let's
just disable it for now.

default.yml

@@ -166,7 +166,7 @@ Lint/UnusedMethodArgument:
 
 Lint/BinaryOperatorWithIdenticalOperands:
   Description: 'This cop checks for places where binary operator has identical operands.'
-  Enabled: true
+  Enabled: false
 
 Lint/UselessElseWithoutRescue:
   Description: 'Checks for useless `else` in `begin..end` without `rescue`.'