Support swift 6 (#267)

Author: camden-king

GTMAppAuth/Sources/KeychainStore/GTMOAuth2Compatibility.swift

@@ -108,10 +108,10 @@ public final class GTMOAuth2Compatibility: NSObject {
     return originalString.addingPercentEncoding(withAllowedCharacters: urlQueryCharacters)
   }
 
-  private static var googleAuthorizationURL = URL(string: "https://accounts.google.com/o/oauth2/v2/auth")!
+  private static let googleAuthorizationURL = URL(string: "https://accounts.google.com/o/oauth2/v2/auth")!
   static let googleTokenURL = URL(string: "https://www.googleapis.com/oauth2/v4/token")!
-  static var googleRevocationURL = URL(string: "https://accounts.google.com/o/oauth2/revoke")!
-  static var googleUserInfoURL = URL(string: "https://www.googleapis.com/oauth2/v3/userinfo")!
+  static let googleRevocationURL = URL(string: "https://accounts.google.com/o/oauth2/revoke")!
+  static let googleUserInfoURL = URL(string: "https://www.googleapis.com/oauth2/v3/userinfo")!
   static var nativeClientRedirectURI: String {
     return oobString
   }

GTMAppAuth/Sources/KeychainStore/KeychainAttribute.swift

@@ -18,9 +18,9 @@ import Foundation
 
 /// The Keychain attribute used to configure the way the keychain stores your items.
 @objc(GTMKeychainAttribute)
-public final class KeychainAttribute: NSObject {
+public final class KeychainAttribute: NSObject, Sendable {
   /// An enumeratiion listing the various attributes used to configure the Keychain.
-  public enum Attribute {
+  public enum Attribute: Sendable {
     /// Indicates whether to use the legacy file-based keychain on macOS.
     ///
     /// This attribute will set `kSecUseDataProtectionKeychain` as `false` in the Keychain query.