Fix light/dark mode documentation toggle (#1760)

Co-authored-by: Douwe Maan <douwe@pydantic.dev>

Author: Viicos

mkdocs.yml

@@ -105,25 +105,24 @@ theme:
   custom_dir: docs/.overrides
   palette:
     - media: "(prefers-color-scheme)"
-      scheme: default
       primary: pink
       accent: pink
       toggle:
-        icon: material/lightbulb
+        icon: material/brightness-auto
         name: "Switch to light mode"
     - media: "(prefers-color-scheme: light)"
       scheme: default
       primary: pink
       accent: pink
       toggle:
-        icon: material/lightbulb-outline
+        icon: material/brightness-7
         name: "Switch to dark mode"
     - media: "(prefers-color-scheme: dark)"
       scheme: slate
       primary: pink
       accent: pink
       toggle:
-        icon: material/lightbulb-auto-outline
+        icon: material/brightness-4
         name: "Switch to system preference"
   features:
     - search.suggest