try to use sphinx pre built

flake.nix

@@ -25,7 +25,7 @@
             let
               fixSphinx = ps: 
                 if ps ? sphinx 
-                then ps.sphinx.override { preferWheel = true; }
+                then ps.sphinx.overridePythonAttrs (old: { version = "7.2.6"; })
                 else ps.sphinx;
             in
               pythonPackages;