chore(deps): update dependency sphinx to v8 (#428)

Author: renovate[bot]

setup.py

@@ -41,7 +41,7 @@
     ],
     extras_require={
         "docs": [
-            "sphinx>=7.4,<7.5",
+            "sphinx>=8,<8.1",
             "sphinx-rtd-theme>=3,<3.1",
             "myst-parser>=4,<4.1",
             "watchdog>=5,<5.1",