[Auth] Query with kSecAttrSynchronizable when auth sharing enabled (#13642)

Author: ncooke3

FirebaseAuth/CHANGELOG.md

@@ -1,3 +1,8 @@
+# Unreleased
+- [Fixed] Restore Firebase 10 behavior by querying with the
+  `kSecAttrSynchronizable` key when auth state is set to be shared across
+  devices. (#13584)
+
 # 11.2.0
 - [Fixed] Fixed crashes that could occur in Swift continuation blocks running in the Xcode 16
   betas. (#13480)

FirebaseAuth/Sources/Swift/SystemService/AuthStoredUserManager.swift

@@ -161,6 +161,10 @@ class AuthStoredUserManager {
     ]
     query[kSecUseDataProtectionKeychain as String] = true
 
+    if shareAuthStateAcrossDevices {
+      query[kSecAttrSynchronizable as String] = true
+    }
+
     return query
   }
 }