fix(storage, ios): dont enumerate on dictionary being mutated (#5455)

Avoid a possible crash during storage dealloc by iterating on a copy of the
array being mutated instead of the array itself

Author: danielhover

packages/storage/ios/RNFBStorage/RNFBStorageModule.m

@@ -61,13 +61,13 @@ - (id)init {
 }
 
 - (void)dealloc {
-  for (NSString *key in PENDING_TASKS) {
+  for (NSString *key in [PENDING_TASKS allKeys]) {
     [PENDING_TASKS removeObjectForKey:key];
   }
 }
 
 - (void)invalidate {
-  for (NSString *key in PENDING_TASKS) {
+  for (NSString *key in [PENDING_TASKS allKeys]) {
     [PENDING_TASKS removeObjectForKey:key];
   }
 }