Replace `str.index` with `str.find`

[tomasr8]

str.index raises a ValueError when the substring is not found so there is no way to even check the return value as the code currently tries to do. Replacing it with str.find makes the code work as intended.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.28%. Comparing base (f91754b) to head (be2709c). Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1130      +/-   ##
==========================================
+ Coverage   91.26%   91.28%   +0.02%     
==========================================
  Files          27       27              
  Lines        4602     4602              
==========================================
+ Hits         4200     4201       +1     
+ Misses        402      401       -1     

Flag	Coverage Δ
macos-12-3.10	90.09% <100.00%> (+0.02%)	:arrow_up:
macos-12-3.11	90.02% <100.00%> (+0.02%)	:arrow_up:
macos-12-3.12	90.19% <100.00%> (+0.02%)	:arrow_up:
macos-12-3.13-dev	89.72% <100.00%> (+0.02%)	:arrow_up:
macos-12-3.8	90.01% <100.00%> (+0.02%)	:arrow_up:
macos-12-3.9	90.01% <100.00%> (+0.02%)	:arrow_up:
macos-12-pypy3.10	90.09% <100.00%> (+0.02%)	:arrow_up:
ubuntu-22.04-3.10	90.11% <100.00%> (+0.02%)	:arrow_up:
ubuntu-22.04-3.11	90.04% <100.00%> (+0.02%)	:arrow_up:
ubuntu-22.04-3.12	90.22% <100.00%> (+0.02%)	:arrow_up:
ubuntu-22.04-3.13-dev	89.74% <100.00%> (+0.02%)	:arrow_up:
ubuntu-22.04-3.8	90.04% <100.00%> (+0.02%)	:arrow_up:
ubuntu-22.04-3.9	90.04% <100.00%> (+0.02%)	:arrow_up:
ubuntu-22.04-pypy3.10	90.11% <100.00%> (+0.02%)	:arrow_up:
windows-2022-3.10	90.23% <100.00%> (+0.02%)	:arrow_up:
windows-2022-3.11	90.16% <100.00%> (+0.02%)	:arrow_up:
windows-2022-3.12	90.34% <100.00%> (+0.02%)	:arrow_up:
windows-2022-3.13-dev	89.86% <100.00%> (+0.02%)	:arrow_up:
windows-2022-3.8	90.16% <100.00%> (+0.02%)	:arrow_up:
windows-2022-3.9	90.16% <100.00%> (+0.02%)	:arrow_up:
windows-2022-pypy3.10	90.23% <100.00%> (+0.02%)	:arrow_up:

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