build: bump brew cache to v6 (#38317)

Co-authored-by: trop[bot] <37223003+trop[bot]@users.noreply.github.com>
Co-authored-by: Shelley Vohr <[email protected]>

.circleci/config/base.yml

@@ -357,14 +357,14 @@ step-restore-brew-cache: &step-restore-brew-cache
       - /usr/local/Cellar/gnu-tar
       - /usr/local/bin/gtar
     keys:
-      - v5-brew-cache-{{ arch }}
+      - v6-brew-cache-{{ arch }}
 
 step-save-brew-cache: &step-save-brew-cache
   save_cache:
     paths:
       - /usr/local/Cellar/gnu-tar
       - /usr/local/bin/gtar
-    key: v5-brew-cache-{{ arch }}
+    key: v6-brew-cache-{{ arch }}
     name: Persisting brew cache
 
 step-get-more-space-on-mac: &step-get-more-space-on-mac