Hot fix for feature/update_to_spack_v1: update invalid syntax in mpi.lua

[climbfuji]

Description

In the title. In the last PR, I copied over the comment from the tcl/tk modulefile to the lua/lmod file. This bug will cause failures when trying to load the stack-MPI module.

Dependencies

None

Issues addressed

This bug will cause failures when trying to load the stack-MPI module.

Applications affected

All

Systems affected

All

Testing

• CI: Note whether the automatic tests (GitHub actions tests that run automatically for every commit) pass or not
  • GitHub actions CI tests pass
  • GitHub actions CI tests do not pass (provide explanation)
  • GitHub actions CI tests skipped (provide explanation if necessary)
• New tests added: List and describe any new tests added to GitHub actions
  • ...
• Additional testing: Add information on any additional tests conducted
  • ...

Checklist

• This PR addresses one issue/problem/enhancement or has a very good reason for not doing so.
• These changes have been tested on the affected systems and applications. (NRL Atlantis)
• All dependency PRs/issues have been resolved and this PR can be merged.
• All necessary updates to the documentation on readthedocs are included in this PR
  • For site config updates, check in particular doc/source/PreConfiguredSites.rst and doc/source/MaintainersSection.rst
• All necessary updates to the spack-stack wiki will be made when this PR is merged