Fix Julia 1.11 errors

[MichaelHatherly]

Fixes #190.

There's a number of other test failures due to assumptions hardcoded in specific tests that will also need to be addressed before CI will pass.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 13 lines in your changes missing coverage. Please review.

Project coverage is 51.59%. Comparing base (4efa39a) to head (f1b5e21).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/QuartoNotebookWorker/src/render.jl	0.00%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #191      +/-   ##
==========================================
+ Coverage   51.51%   51.59%   +0.07%     
==========================================
  Files          30       30              
  Lines        1283     1285       +2     
==========================================
+ Hits          661      663       +2     
  Misses        622      622              

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