C-API specs in :next specs do not work

* Because `#ifdef RUBY_VERSION_IS_3_2` uses the real Ruby version
  and is not affected by `PRETEND_RUBY_VERSION`.

Author: eregon

doc/contributor/workflow.md

@@ -322,6 +322,9 @@ When working on a feature from the next version of Ruby, add the spec file in
 the corresponding files list in `spec/truffleruby.next-specs` so that the specs
 are run in CI too.
 
+However this does not work for C-API specs,
+because those use `#ifdef RUBY_VERSION_IS_3_2` and that version cannot be faked.
+
 ## How to fix a failing MRI test
 
 Remove the exclusion of either the file (`test/mri/failing.exclude`) or the

spec/truffleruby.next-specs

@@ -37,6 +37,5 @@ spec/ruby/core/module/refinements_spec.rb
 spec/ruby/core/module/undefined_instance_methods_spec.rb
 spec/ruby/core/refinement/refined_class_spec.rb
 spec/ruby/core/module/used_refinements_spec.rb
-spec/ruby/optional/capi/hash_spec.rb
 
 spec/ruby/core/thread/each_caller_location_spec.rb