Remove some DeprecationWarnings

[EvanBldy]

Summarize your change.

During the tests some DeprecationWarnings pop up. I only fix them.

Reference associated tests.

For example here you see the DeprecationWarnings : https://github.com/AcademySoftwareFoundation/OpenTimelineIO/actions/runs/7483248301/job/20368203066?pr=1669#step:9:18

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (d98f657) 79.84% compared to head (0f79837) 79.84%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1688   +/-   ##
=======================================
  Coverage   79.84%   79.84%           
=======================================
  Files         197      197           
  Lines       21792    21792           
  Branches     4358     4358           
=======================================
  Hits        17399    17399           
  Misses       2232     2232           
  Partials     2161     2161           

Flag	Coverage Δ
py-unittests	79.84% <75.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...-opentimelineio/opentimelineio/adapters/fcp_xml.py	88.40% <100.00%> (ø)
...ontrib/opentimelineio_contrib/adapters/fcpx_xml.py	91.29% <66.66%> (ø)

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[jminor]

From meeting discussion: we plan to land this and then copy it over into the new FCP XML adapter repo.