Fix #8226: Prevent HHWs from being crewed

[psikomonkie]

Fixes #8226

Don't merge until MegaMek/megamek#7651 is merged.

[IllianiBird]

You might need to update this PR when you merge the MM half, for GitHub to pick up that it's all kosher. But zero issues insofar as I can see them.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 11.72%. Comparing base (cddd9fc) to head (f130d04).
⚠️ Report is 21 commits behind head on main.

Files with missing lines	Patch %	Lines
MekHQ/src/mekhq/campaign/unit/Unit.java	0.00%	4 Missing ⚠️
...kHQ/src/mekhq/campaign/ResolveScenarioTracker.java	0.00%	1 Missing ⚠️
.../src/mekhq/campaign/mission/CrewSkillUpgrader.java	0.00%	0 Missing and 1 partial ⚠️
MekHQ/src/mekhq/gui/adapter/TOEMouseAdapter.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8270      +/-   ##
============================================
- Coverage     11.73%   11.72%   -0.01%     
+ Complexity     7536     7532       -4     
============================================
  Files          1271     1271              
  Lines        162721   162724       +3     
  Branches      24515    24515              
============================================
- Hits          19095    19082      -13     
- Misses       141628   141644      +16     
  Partials       1998     1998              

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