add character-ps to Grandfathered deps

as commented: 'aeson' & 'attoparsec-aeson' now depend on this library;
while not present before it is a direct dependency of 'aeson', so i'm
counting that as "grandfathering" it in

build-constraints.yaml

@@ -5459,6 +5459,7 @@ packages:
         - cereal
         - cereal-text
         - cereal-vector
+        - character-ps # dependency of 'aeson' & 'attoparsec-aeson' as of 2.2.2.0
         - chunked-data
         - cipher-aes128 < 0 # 0.7.0.6 compile fail
         - cipher-blowfish < 0 # 0.0.3 compile fail