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/agit/agit.go

@@ -80,7 +80,7 @@ func ProcReceive(ctx context.Context, repo *repo_model.Repository, gitRepo *git.
 			continue
 		}
 
-		headBranch := ""
+		var headBranch string
 		userName := strings.ToLower(opts.UserName)
 
 		if len(curentTopicBranch) == 0 {
@@ -104,7 +104,7 @@ func ProcReceive(ctx context.Context, repo *repo_model.Repository, gitRepo *git.
 
 			// create a new pull request
 			if len(title) == 0 {
-				has := false
+				var has bool
 				title, has = opts.GitPushOptions["title"]
 				if !has || len(title) == 0 {
 					commit, err := gitRepo.GetCommit(opts.NewCommitIDs[i])