[Firestore] Make Swift code compatible with Xcode 13.3.1 (#11497)

Author: ncooke3

Firestore/Swift/CHANGELOG.md

@@ -1,4 +1,4 @@
-# unreleased
+# 10.12.0
 - [added] Added support animations on the `@FirestoreQuery` property wrapper.
 
 # 10.9.0

Firestore/Swift/Source/PropertyWrapper/FirestoreQueryObservable.swift

@@ -41,7 +41,7 @@ internal class FirestoreQueryObservable<T>: ObservableObject {
     items = []
     self.configuration = configuration
     setupListener = createListener { [weak self] querySnapshot, error in
-      guard let self else { return }
+      guard let self = self else { return }
       if let error = error {
         self.animated {
           self.items = []
@@ -98,7 +98,7 @@ internal class FirestoreQueryObservable<T>: ObservableObject {
     items = .success([])
     self.configuration = configuration
     setupListener = createListener { [weak self] querySnapshot, error in
-      guard let self else { return }
+      guard let self = self else { return }
       if let error = error {
         self.animated {
           self.items = .failure(error)