Extract single element of array before declaring amplitude of adjoint source

[oskooi]

A unit test for the adjoint solver (test_two_objfunc of test_adjoint_solver.py) recently started failing during CI for Python 3.11 due to the following line:

meep/python/source.py

Line 127 in e407a5a

self.amplitude = complex(amplitude)

The error is triggered when amplitude is passed to the Source constructor as a Numpy array with a single element. Python's complex function supports 0-dimensional Numpy arrays. The fix simply involves extracting the element of the array before applying the complex function.

(It is not clear why this error was triggered recently and only for Python 3.11.)

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.90%. Comparing base (f29a8c7) to head (bb8e21e).
⚠️ Report is 98 commits behind head on master.
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3129      +/-   ##
==========================================
+ Coverage   73.81%   73.90%   +0.09%     
==========================================
  Files          18       18              
  Lines        5423     5454      +31     
==========================================
+ Hits         4003     4031      +28     
- Misses       1420     1423       +3     

Files with missing lines	Coverage Δ
python/source.py	94.11% <100.00%> (+0.03%)	⬆️

... and 2 files with indirect coverage changes

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