deps: Update dependency sphinx to v8 (data-apis#261)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

docs/requirements.txt

@@ -1,5 +1,5 @@
 furo>=2024.8.6
 myst_parser>=4.0.1
-sphinx>=7.4.7
+sphinx>=8.2.3
 sphinx_autodoc_typehints
 sphinx_copybutton