Correctly detect mutation on serialized columns mapping to binary

[sgrif]

Fixes #16701

[rafaelfranca]

PostgreSQL build is broken.

[felixbuenemann]

Maybe the failures are because postgres uses Bytea type for binary columns which overrides type_cast_from_databaseof Type::Binary:
activerecord/lib/active_record/connection_adapters/postgresql/oid/bytea.rb

Btw. legacy mysql adapter also failed on travis, but it seems unrelated (segfault).

[felixbuenemann]

@sgrif not sure I fully understand your changes, but maybe this would work:

# ActiveRecord::ConnectionAdapters::PostgreSQL::OID::Bytea
def type_cast_from_database(value)
  return if value.nil?
  Type::Binary::Data.new(PGconn.unescape_bytea(super))
end

This way the return type of type_cast_from_database wouldn't differ for Bytea.

[sgrif]

Updated