[Database] Mark 'FIRDataSnapshot' as Sendable (#14439)

Author: ncooke3

FirebaseDatabase/CHANGELOG.md

@@ -3,6 +3,7 @@
   Socket Rocket implementation instead of `NSURLSessionWebSocket`. Note that
   this may expose a Thread Performance Checker Warning (#12883).
   (#14188, #13877, #13855, #13529)
+- [fixed] Added `Sendable` conformance to `DataSnapshot` (#14369).
 
 # 11.2.0
 - [fixed] Fix temporary disconnects when the app goes inactive. The issue was

FirebaseDatabase/Sources/Public/FirebaseDatabase/FIRDataSnapshot.h

@@ -30,6 +30,7 @@ NS_ASSUME_NONNULL_BEGIN
  * location. They can't be modified and will never change. To modify data at a
  * location, use a DatabaseReference (e.g. with `setValue(_:)`).
  */
+NS_SWIFT_SENDABLE
 NS_SWIFT_NAME(DataSnapshot)
 @interface FIRDataSnapshot : NSObject