Fix query cache for pinned connections in multi threaded transactional tests

Ref: rails/rails#55703

Author: aidanharan

test/support/core_ext/query_cache.rb

@@ -23,7 +23,7 @@ module SqlIgnoredCache
   def cache_sql(sql, name, binds)
     result = super
 
-    @query_cache.instance_variable_get(:@map).delete_if do |cache_key, _v|
+    query_cache.instance_variable_get(:@map).delete_if do |cache_key, _v|
       # Query cache key generated by `sql` or `[sql, binds]`, so need to retrieve `sql` for both cases.
       cache_key_sql = Array(cache_key).first
       Regexp.union(IGNORED_SQL).match?(cache_key_sql)