Bump Homebrew cache key (#27764)

Summary:
Trivial: bump Circle CI Homebrew cache key to move past cache error in CI builds.

Changelog:
[Internal] - Bump Homebrew cache key on Circle CI

Pull Request resolved: https://github.com/facebook/react-native/pull/27764

Differential Revision: D19401723

Pulled By: hramos

fbshipit-source-id: cec18ea68ac141ab85ad694ac261d98cbf0e4440

.circleci/config.yml

@@ -109,13 +109,13 @@ commands:
     steps:
       - restore_cache:
           keys:
-            - v2-brew
+            - v3-brew
       - steps: << parameters.steps >>
       - save_cache:
           paths:
             - /usr/local/Homebrew
             - ~/Library/Caches/Homebrew
-          key: v2-brew
+          key: v3-brew
 
   with_pods_cache_span:
     parameters: