Before 34cc301, type casting by boolean attribute when querying is a
no-op, so finding by truthy boolean string (i.e.
`where(value: "true") # => value = 'true'`) didn't work as expected
(matches it to FALSE in MySQL #32624). By type casting is ensured, a
value on boolean attribute is always serialized to TRUE or FALSE.
In PostgreSQL, `where(value: :false) # => value = 'false'` was a valid
SQL, so 34cc301 is a regresson for PostgreSQL since all symbol values
are serialized as TRUE.
I'd say using `:false` is mostly a developer's mistake (user's input
basically comes as a string), but `:false` on boolean attribute is
serialized as TRUE is not a desirable behavior for anybody.
This allows falsy boolean symbols as false, i.e.
`klass.create(value: :false).value? # => false` and
`where(value: :false) # => value = FALSE`.
Fixes#35676.
`QueryAttribute#value_for_database` calls only `type.serialize`, and
`Boolean#serialize` is a no-op unlike other attribute types.
It caused the issue #32624. Whether or not `serialize` will invoke
`cast` is undefined in our test cases, but it actually does not work
properly unless it does so for now.
Fixes#32624.
