Convert keys to binary in the Redis cache store

Fix encoding errors when using the pure-Ruby Redis driver instead of Hiredis. Dodge incompatibilities between UTF-8 and arbitrary value encodings, which rear their heads when the Redis driver tries to build a single command string from incompatibly-encoded keys and values.

activesupport/lib/active_support/cache/redis_cache_store.rb

@@ -363,7 +363,7 @@ def write_multi_entries(entries, expires_in: nil, **options)
 
         # Truncate keys that exceed 1kB.
         def normalize_key(key, options)
-          truncate_key super
+          truncate_key super.b
         end
 
         def truncate_key(key)