feat: migrate action secrets to keying to store them more securely (#8692)

- Use the keying module, that was introduced in forgejo/forgejo#5041, to store action secrets safely and securely in the database.
- Introduce a central function that sets the secret, `SetSecret` and let the caller do the update call. This is similar to how the twofactor (TOTP) models does it. Ref. https://codeberg.org/forgejo/forgejo/pulls/6074
- Add a relaxed migration, that is run inside a transaction. If it cannot decrypt a action secret, then it's deleted.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/8692
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

models/secret/main_test.go

@@ -0,0 +1,17 @@
+// Copyright 2025 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package secret_test
+
+import (
+	"testing"
+
+	"forgejo.org/models/unittest"
+
+	_ "forgejo.org/models"
+	_ "forgejo.org/models/activities"
+)
+
+func TestMain(m *testing.M) {
+	unittest.MainTest(m)
+}