Add MPI compat workflows.

[vincentmr]

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---

Context:
MPI tests for L-GPU are missing from the compatibility workflows.

Description of the Change:
Add MPI tests in the compatibility workflows.

Benefits:

Possible Drawbacks:

Related GitHub Issues:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ce8597e) 99.00% compared to head (902b349) 99.20%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #536      +/-   ##
==========================================
+ Coverage   99.00%   99.20%   +0.19%     
==========================================
  Files         167      201      +34     
  Lines       22211    26480    +4269     
==========================================
+ Hits        21990    26269    +4279     
+ Misses        221      211      -10     

Files	Coverage Δ
pennylane_lightning/core/_version.py	100.00% <100.00%> (ø)
pennylane_lightning/core/lightning_base.py	100.00% <100.00%> (ø)
...rc/simulators/lightning_gpu/StateVectorCudaMPI.hpp	99.62% <100.00%> (ø)
...lightning_gpu/algorithms/AdjointJacobianGPUMPI.hpp	96.66% <ø> (ø)
...rs/lightning_gpu/observables/ObservablesGPUMPI.hpp	100.00% <100.00%> (ø)
...rc/simulators/lightning_gpu/utils/MPILinearAlg.hpp	100.00% <100.00%> (ø)
pennylane_lightning/lightning_gpu/lightning_gpu.py	85.94% <100.00%> (-1.72%)	⬇️

... and 53 files with indirect coverage changes

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[mlxd]

Happy to approve, but let's merge after #538 and then after the CI goes green.

[multiphaseCFD]

Looks good to me! Thanks!