[FIAM] Fix an objc_retain crash (#12395)

Author: paulb777

FirebaseInAppMessaging/CHANGELOG.md

@@ -1,3 +1,6 @@
+# 10.22.0
+- [fixed] Fixed an `objc_retain` crash. (#12393)
+
 # 10.17.0
 - [deprecated] All of the public API from `FirebaseInAppMessagingSwift` can now
   be accessed through the `FirebaseInAppMessaging` module. Therefore,

FirebaseInAppMessaging/Sources/Flows/FIRIAMMessageClientCache.m

@@ -126,7 +126,9 @@ - (void)setupAnalyticsEventListening {
 }
 
 - (BOOL)hasTestMessage {
-  return self.testMessages.count > 0;
+  @synchronized(self) {
+    return self.testMessages.count > 0;
+  }
 }
 
 - (nullable FIRIAMMessageDefinition *)nextOnAppLaunchDisplayMsg {
@@ -135,7 +137,7 @@ - (nullable FIRIAMMessageDefinition *)nextOnAppLaunchDisplayMsg {
 
 - (nullable FIRIAMMessageDefinition *)nextOnAppOpenDisplayMsg {
   @synchronized(self) {
-    // always first check test message which always have higher prirority
+    // always first check test message which always have higher priority
     if (self.testMessages.count > 0) {
       FIRIAMMessageDefinition *testMessage = self.testMessages[0];
       // always remove test message right away when being fetched for display