Add more linters to improve code readability (#19989)

Add nakedret, unconvert, wastedassign, stylecheck and nolintlint linters to improve code readability

- nakedret - https://github.com/alexkohler/nakedret - nakedret is a Go static analysis tool to find naked returns in functions greater than a specified function length.
- unconvert - https://github.com/mdempsky/unconvert - Remove unnecessary type conversions
- wastedassign - https://github.com/sanposhiho/wastedassign -  wastedassign finds wasted assignment statements.
- notlintlint -  Reports ill-formed or insufficient nolint directives
- stylecheck - https://staticcheck.io/docs/checks/#ST - keep style consistent
  - excluded: [ST1003 - Poorly chosen identifier](https://staticcheck.io/docs/checks/#ST1003) and [ST1005 - Incorrectly formatted error string](https://staticcheck.io/docs/checks/#ST1005)

services/issue/assignee.go

@@ -59,7 +59,7 @@ func ToggleAssignee(issue *issues_model.Issue, doer *user_model.User, assigneeID
 
 	notification.NotifyIssueChangeAssignee(doer, issue, assignee, removed, comment)
 
-	return
+	return removed, comment, err
 }
 
 // ReviewRequest add or remove a review request from a user for this PR, and make comment for it.
@@ -78,7 +78,7 @@ func ReviewRequest(issue *issues_model.Issue, doer, reviewer *user_model.User, i
 		notification.NotifyPullReviewRequest(doer, issue, reviewer, isAdd, comment)
 	}
 
-	return
+	return comment, err
 }
 
 // IsValidReviewRequest Check permission for ReviewRequest
@@ -262,5 +262,5 @@ func TeamReviewRequest(issue *issues_model.Issue, doer *user_model.User, reviewe
 		notification.NotifyPullReviewRequest(doer, issue, member, isAdd, comment)
 	}
 
-	return
+	return comment, err
 }