tools: enable no-cond-assign-ESLint rule

no-cond-assign is one of the few ESLint recommended rules that we have
turned off. This change enables the rule.

PR-URL: #41614
Reviewed-By: Tobias Nießen <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>

Author: Trott

.eslintrc.js

@@ -295,7 +295,6 @@ module.exports = {
     'valid-typeof': ['error', { requireStringLiterals: true }],
 
     // ESLint recommended rules that we disable
-    'no-cond-assign': 'off',
     'no-empty': 'off',
     'no-inner-declarations': 'off',
     'no-prototype-builtins': 'off',