Fix incorrect action duration time when rerun the job before executed once (#28364)

Fix #28323
Reason was mentioned here:
https://github.com/go-gitea/gitea/issues/28323#issuecomment-1841867298

### Changes: (maybe breaking)
We can rerun jobs in Gitea, so there will be some problems in
calculating duration time.
In this PR, I use the exist `Started` and `Stopped` column to record the
last run time instead of the total time,
and add a new `PreviousDuration` column to record the previous duration
time.
You can also check the cost time of last run:

![image](https://github.com/go-gitea/gitea/assets/18380374/2ca39145-2c92-401a-b78b-43164f7ae061)

models/migrations/v1_22/v285.go

@@ -0,0 +1,18 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_22 //nolint
+
+import (
+	"time"
+
+	"xorm.io/xorm"
+)
+
+func AddPreviousDurationToActionRun(x *xorm.Engine) error {
+	type ActionRun struct {
+		PreviousDuration time.Duration
+	}
+
+	return x.Sync(&ActionRun{})
+}