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/web/repo/view.go

@@ -353,7 +353,7 @@ func renderReadmeFile(ctx *context.Context, readmeFile *namedBlob, readmeTreelin
 
 	if markupType := markup.Type(readmeFile.name); markupType != "" {
 		ctx.Data["IsMarkup"] = true
-		ctx.Data["MarkupType"] = string(markupType)
+		ctx.Data["MarkupType"] = markupType
 		var result strings.Builder
 		err := markup.Render(&markup.RenderContext{
 			Ctx:          ctx,