pyproject: Update docs dependencies

With work beginning on general docs and Sphinx, refresh the docs
versions to the latest available.  The RTD theme is left open-ended with
no maximum version.

Author: akkornel

pyproject.toml

@@ -75,8 +75,8 @@ dependencies = [
 # 3: Optional dependencies.
 [project.optional-dependencies]
 docs = [
-	"sphinx <5.0, >=4.5.0",
-	"sphinx-rtd-theme",
+	"sphinx <9.0, >=8.1.3",
+	"sphinx-rtd-theme >=3.0.2",
 ]
 
 test = [