[Glitch] Refactor PrivacyDropdown to TypeScript

Port 8a235dd187 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/features/ui/components/boost_modal.tsx

@@ -53,7 +53,10 @@ export const BoostModal: React.FC<{
   }, [onClose]);
 
   const findContainer = useCallback(
-    () => document.getElementsByClassName('modal-root__container')[0],
+    () =>
+      document.getElementsByClassName(
+        'modal-root__container',
+      )[0] as HTMLDivElement,
     [],
   );