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/web.go

@@ -138,7 +138,7 @@ func Routes() *web.Route {
 
 	// redirect default favicon to the path of the custom favicon with a default as a fallback
 	routes.Get("/favicon.ico", func(w http.ResponseWriter, req *http.Request) {
-		http.Redirect(w, req, path.Join(setting.StaticURLPrefix, "/assets/img/favicon.png"), 301)
+		http.Redirect(w, req, path.Join(setting.StaticURLPrefix, "/assets/img/favicon.png"), http.StatusMovedPermanently)
 	})
 
 	common := []interface{}{}
@@ -1121,7 +1121,7 @@ func RegisterRoutes(m *web.Route) {
 			}
 
 			repo.MustBeNotEmpty(ctx)
-			return
+			return cancel
 		})
 
 		m.Group("/pulls/{index}", func() {