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/issue_test.go

@@ -129,7 +129,7 @@ func TestUpdateIssueCols(t *testing.T) {
 	issue.Content = "This should have no effect"
 
 	now := time.Now().Unix()
-	assert.NoError(t, updateIssueCols(db.GetEngine(db.DefaultContext), issue, "name"))
+	assert.NoError(t, updateIssueCols(db.DefaultContext, issue, "name"))
 	then := time.Now().Unix()
 
 	updatedIssue := unittest.AssertExistsAndLoadBean(t, &Issue{ID: issue.ID}).(*Issue)