Fix WaitGate for multiple qubits in cirq_google proto

[dstrain115]

• WaitGate operations with multiple qubits need to specify the num_qubits parameter.
• This PR fixes this and adds an appropriate test case.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.14%. Comparing base (0eea89e) to head (494c273).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7189      +/-   ##
==========================================
- Coverage   98.14%   98.14%   -0.01%     
==========================================
  Files        1100     1100              
  Lines       96191    96191              
==========================================
- Hits        94409    94408       -1     
- Misses       1782     1783       +1     

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