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)

routers/private/hook_pre_receive.go

@@ -248,7 +248,7 @@ func preReceiveBranch(ctx *preReceiveContext, oldCommitID, newCommitID, refFullN
 	}
 
 	// 5. Check if the doer is allowed to push
-	canPush := false
+	var canPush bool
 	if ctx.opts.DeployKeyID != 0 {
 		canPush = !changedProtectedfiles && protectBranch.CanPush && (!protectBranch.EnableWhitelist || protectBranch.WhitelistDeployKeys)
 	} else {

routers/private/manager_process.go

@@ -34,7 +34,7 @@ func Processes(ctx *context.PrivateContext) {
 
 	var processes []*process_module.Process
 	goroutineCount := int64(0)
-	processCount := 0
+	var processCount int
 	var err error
 	if stacktraces {
 		processes, processCount, goroutineCount, err = process_module.GetManager().ProcessStacktraces(flat, noSystem)

routers/private/serv.go

@@ -142,7 +142,7 @@ func ServCommand(ctx *context.PrivateContext) {
 		if repo_model.IsErrRepoNotExist(err) {
 			repoExist = false
 			for _, verb := range ctx.FormStrings("verb") {
-				if "git-upload-pack" == verb {
+				if verb == "git-upload-pack" {
 					// User is fetching/cloning a non-existent repository
 					log.Warn("Failed authentication attempt (cannot find repository: %s/%s) from %s", results.OwnerName, results.RepoName, ctx.RemoteAddr())
 					ctx.JSON(http.StatusNotFound, private.ErrServCommand{