Redis cache store: fix constructing with a Redis instance

Since `Redis#call` duck types as a Proc, we'd call `#call` on it,
thinking it's a Proc. Fixed by check for the Proc explicitly instead of
duck typing on `#call`.

References #32233

activesupport/lib/active_support/cache/redis_cache_store.rb

@@ -118,7 +118,7 @@ module ActiveSupport
         def build_redis(redis: nil, url: nil, **redis_options) #:nodoc:
           urls = Array(url)
 
-          if redis.respond_to?(:call)
+          if redis.is_a?(Proc)
             redis.call
           elsif redis
             redis

activesupport/test/cache/stores/redis_cache_store_test.rb

@@ -95,6 +95,12 @@ module ActiveSupport::Cache::RedisCacheStoreTests
       end
     end
 
+    test "instance of Redis uses given instance" do
+      redis_instance = Redis.new
+      @cache = build(redis: redis_instance)
+      assert_same @cache.redis, redis_instance
+    end
+
     private
       def build(**kwargs)
         ActiveSupport::Cache::RedisCacheStore.new(driver: DRIVER, **kwargs).tap do |cache|