Fix CheckRepoStats and reuse it during migration (#18264)

The CheckRepoStats function missed the following counters:

- label num_closed_issues & num_closed_pulls
- milestone num_closed_issues & num_closed_pulls

The update SQL statements for updating the repository
num_closed_issues & num_closed_pulls fields were repeated in three
functions (repo.CheckRepoStats, migrate.insertIssues and
models.Issue.updateClosedNum) and were moved to a single helper.

The UpdateRepoStats is implemented and called in the Finish migration method so that it happens immediately instead of wating for the
CheckRepoStats to run.

Signed-off-by: Loïc Dachary loic@dachary.org

---
[source](https://lab.forgefriends.org/forgefriends/forgefriends/-/merge_requests/34)

models/repo_test.go

@@ -17,6 +17,11 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+func TestCheckRepoStats(t *testing.T) {
+	assert.NoError(t, unittest.PrepareTestDatabase())
+	assert.NoError(t, CheckRepoStats(db.DefaultContext))
+}
+
 func TestWatchRepo(t *testing.T) {
 	assert.NoError(t, unittest.PrepareTestDatabase())
 	const repoID = 3