Bump queue warning threshold to 60

Aligns with J2K.

app/src/main/java/eu/kanade/tachiyomi/data/library/LibraryUpdateService.kt

@@ -574,4 +574,4 @@ class LibraryUpdateService(
     }
 }
 
-const val PER_SOURCE_QUEUE_WARNING_THRESHOLD = 50
+const val PER_SOURCE_QUEUE_WARNING_THRESHOLD = 60