fix bug in masked, multi-dimensional state space multi-threaded envs

[Graeme22]

This fixes what appears to be a copy/paste bug that affects multi-threaded envs where the state space of the wrapped environment has different dimensionality than the action space of that environment.

For an example environment that this breaks, see https://github.com/Graeme22/rlskedge

PR Checklist

• Update NEWS.md?
• Unit tests for all structs / functions?
• Integration and correctness tests using a simple env?
• PR Review?
• Add or update documentation?
• Write docstrings for new methods?

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 0.04%. Comparing base (ea00fdf) to head (32604f2).
⚠️ Report is 116 commits behind head on main.

Files with missing lines	Patch %	Lines
...src/algorithms/policy_gradient/multi_thread_env.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #900       +/-   ##
==========================================
- Coverage   24.49%   0.04%   -24.46%     
==========================================
  Files         219     207       -12     
  Lines        7687    7361      -326     
==========================================
- Hits         1883       3     -1880     
- Misses       5804    7358     +1554     

Files with missing lines	Coverage Δ
...src/algorithms/policy_gradient/multi_thread_env.jl	0.00% <0.00%> (ø)

... and 63 files with indirect coverage changes

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[jeremiahpslewis]

@Graeme22 This looks like a good catch, thanks! Would you be able to contribute a test that would have caught the issue?