fix vkCmdDrawMeshIndirect() validation using wrong type

[Firestar99]

1. Update documentation to reflect any user-facing changes - in this repository.

2. Make sure that the changes are covered by unit-tests.

3. Run cargo clippy on the changes.

4. Run cargo +nightly fmt on the changes.

5. Please put changelog entries in the description of this Pull Request
   if knowledge of this change could be valuable to users. No need to put the
   entries to the changelog directly, they will be transferred to the changelog
   file by maintainers right after the Pull Request merge.

   Please remove any items from the template below that are not applicable.

6. Describe in common words what is the purpose of this change, related
   GitHub Issues, and highlight important implementation aspects.

Changelog:

### Bugs fixed
- fixed `vkCmdDrawMeshIndirect` always returning a validation error 

[Rua]

Oops! Thanks for the fix!

[marc0246]

Sidenote: ext_mesh_shader support isn't released yet. There's not going to be a changelog entry.