fix: update key to string for 'getPublicScreenTimeData' function

Author: 0xbrayo

src/firebase/data.ts

@@ -92,7 +92,7 @@ export async function getScreenTimeData(
 
 export async function getPublicScreenTimeData(
   since: Date | null = null
-): Promise<{ [key: number]: ScreenTimeSummary[] } | null> {
+): Promise<{ [key: string]: ScreenTimeSummary[] } | null> {
   // Returns all public screentime data, for all users, since `since`, aggregated by user
   const q = query(
     collection(db, 'screentime'),