Fix: sphinx version to python 3.8

Author: Onimock

requirements-dev.txt

@@ -9,6 +9,7 @@ flake8>=7.1.1
 black>=24.8.0
 isort==5.13.2
 flake8-pyproject>=1.2.3
-sphinx>=7.2.6
+sphinx>=6.2.1,<7.0.0; python_version < '3.9'
+sphinx>=7.2.6; python_version >= '3.9'
 sphinx-rtd-theme>=2.0.0
 livereload>=2.6.3