Add an exception requiring PauliStringPhasors only in the left circuit argument for contrib.paulistring.move_pauli_strings_into_circuit.

[Acciaccatura]

As the title says.

• No tests exist for this change (AFAIK), perhaps we should add one? If so, I may need some guidance on what to test for as my QC knowledge is lacking.
• Same with adding a docstring - shall we explicitly state what this function is doing, and/or what it requires, or is it OK to leave it as-is?

Fixes #7934

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.63%. Comparing base (096fe82) to head (b62cda4).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7985      +/-   ##
==========================================
- Coverage   99.63%   99.63%   -0.01%     
==========================================
  Files        1110     1110              
  Lines       99755    99771      +16     
==========================================
+ Hits        99394    99409      +15     
- Misses        361      362       +1     

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