Temporarily lock Sphinx to v8.0.2 to resolve docs build failure. (y-s…

…cope#555)

docs/requirements.txt

@@ -2,7 +2,9 @@ myst-parser>=2.0.0
 # Locked to avoid pydata/pydata-sphinx-theme#1676 until its fix is released in a version above
 # 0.15.2
 pydata-sphinx-theme==0.14.4
-sphinx>=7.3.7
+# Locked to avoid the following issue until a fix is released:
+# https://github.com/sphinx-doc/sphinx/issues/13002
+sphinx==8.0.2
 sphinx_design>=0.5.0
 sphinx-copybutton>=0.5.2
 sphinxcontrib-mermaid>=0.9.2