fix: use correct (historical) macOS keychain name

pkg/keychain/keychain_darwin.go

@@ -0,0 +1,30 @@
+// Copyright (c) 2021 Proton Technologies AG
+//
+// This file is part of ProtonMail Bridge.
+//
+// ProtonMail Bridge is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// ProtonMail Bridge is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with ProtonMail Bridge.  If not, see <https://www.gnu.org/licenses/>.
+
+// +build darwin
+
+package keychain
+
+import (
+	"fmt"
+	"strings"
+)
+
+// hostURL uniquely identifies the app's keychain items within the system keychain.
+func hostURL(keychainName string) string {
+	return fmt.Sprintf("ProtonMail%vService", strings.Title(keychainName))
+}