keg: fix Pathname type mismatch in LinkageCacheStore call

Pass `path.to_s` instead of `path` (a Pathname) to
`LinkageCacheStore.new`, matching the pattern used in
`linkage_checker.rb`. The sig on `initialize` correctly requires a
String since the value is used as a JSON-serializable database key.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: costajohnt

Library/Homebrew/keg.rb

@@ -315,7 +315,7 @@ def uninstall(raise_failures: false)
     CacheStoreDatabase.use(:linkage) do |db|
       break unless db.created?
 
-      LinkageCacheStore.new(path, db).delete!
+      LinkageCacheStore.new(path.to_s, db).delete!
     end
 
     FileUtils.rm_r(path)