Fix Undefined symbols issue (#470)

Co-authored-by: Yasser Al-Khder <yasser.alkhder@gmail.com>
Co-authored-by: Brianna Morales <74382627+brnnmrls@users.noreply.github.com>

Package.swift

@@ -71,6 +71,7 @@ let package = Package(
       name: "GoogleSignIn",
       dependencies: [
         .product(name: "AppAuth", package: "AppAuth"),
+        .product(name: "AppAuthCore", package: "AppAuth"),
         .product(name: "AppCheckCore", package: "AppCheck"),
         .product(name: "GTMAppAuth", package: "GTMAppAuth"),
         .product(name: "GTMSessionFetcherCore", package: "GTMSessionFetcher"),