[Infra] Firestore Xcode 26 beta warnings (#15102)

Firestore/Swift/Source/Codable/DocumentReference+Codable.swift

@@ -51,3 +51,4 @@ extension CodableDocumentReference {
 }
 
 extension FirebaseFirestore.DocumentReference: FirebaseFirestore.CodableDocumentReference {}
+extension FirebaseFirestore.DocumentReference: @retroactive Codable {}

Firestore/Swift/Source/Codable/GeoPoint+Codable.swift

@@ -64,3 +64,4 @@ extension CodableGeoPoint {
 
 /** Extends GeoPoint to conform to Codable. */
 extension FirebaseFirestore.GeoPoint: FirebaseFirestore.CodableGeoPoint {}
+extension FirebaseFirestore.GeoPoint: @retroactive Codable {}

Firestore/Swift/Source/Codable/Timestamp+Codable.swift

@@ -60,3 +60,4 @@ extension CodableTimestamp {
 
 /** Extends Timestamp to conform to Codable. */
 extension FirebaseCore.Timestamp: FirebaseFirestore.CodableTimestamp {}
+extension FirebaseCore.Timestamp: @retroactive Codable {}

Firestore/Swift/Source/Codable/VectorValue+Codable.swift

@@ -59,3 +59,4 @@ extension CodableVectorValue {
 
 /** Extends VectorValue to conform to Codable. */
 extension FirebaseFirestore.VectorValue: FirebaseFirestore.CodableVectorValue {}
+extension FirebaseFirestore.VectorValue: @retroactive Codable {}