Fix @rule effect validation for not cacheable types. (pantsbuild#…

…14069)

pantsbuild#13178 added additional validation of use of `Effect`s in `@goal_rules` but it was accidentally unreachable. 

[ci skip-rust]
[ci skip-build-wheels]

src/python/pants/engine/rules.py

@@ -296,8 +296,6 @@ def validate_requirements(
     awaitables: Tuple[AwaitableConstraints, ...],
     cacheable: bool,
 ) -> None:
-    if not cacheable:
-        return
     # TODO: Technically this will also fire for an @_uncacheable_rule, but we don't expose those as
     # part of the API, so it's OK for these errors not to mention them.
     for ty in parameter_types: