docs: modify logo variable

[sdarwin]

When building the docs with Sphinx 8.1.3 there is an error about 'logo'.

Where is the variable originally defined?

The modification in this PR seems to solve the problem.

[mloskot]

Where is the variable originally defined?

Possibly a bug!

Thank you!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.46%. Comparing base (322c4e2) to head (2f470fb).
Report is 14 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #759      +/-   ##
===========================================
+ Coverage    82.12%   82.46%   +0.34%     
===========================================
  Files          117      117              
  Lines         5355     5727     +372     
===========================================
+ Hits          4398     4723     +325     
- Misses         957     1004      +47     

[sdarwin]

Thanks. RemovedInSphinx90Warning warnings (not errors) also appeared. I have not researched them.

writing output... [ 2%] design/basics
/opt/venvboostdocs/lib/python3.12/site-packages/sphinx/builders/html/init.py:1076: RemovedInSphinx90Warning: The str interface for _JavaScript objects is deprecated. Use js.filename instead.
if resource and '://' in otheruri:
/opt/venvboostdocs/lib/python3.12/site-packages/sphinx/util/osutil.py:48: RemovedInSphinx90Warning: The str interface for _JavaScript objects is deprecated. Use js.filename instead.
if to.startswith(SEP):
/opt/venvboostdocs/lib/python3.12/site-packages/sphinx/util/osutil.py:51: RemovedInSphinx90Warning: The str interface for _JavaScript objects is deprecated. Use js.filename instead.
t2 = to.split('#')[0].split(SEP)