Replace Hard-coded HTTP Verbs with Constants (#27219)

* Replace hard-coded HTTP verbs with constants in `net/http`

server/channels/api4/integration_action.go

@@ -12,10 +12,10 @@ import (
 )
 
 func (api *API) InitAction() {
-	api.BaseRoutes.Post.Handle("/actions/{action_id:[A-Za-z0-9]+}", api.APISessionRequired(doPostAction)).Methods("POST")
+	api.BaseRoutes.Post.Handle("/actions/{action_id:[A-Za-z0-9]+}", api.APISessionRequired(doPostAction)).Methods(http.MethodPost)
 
-	api.BaseRoutes.APIRoot.Handle("/actions/dialogs/open", api.APIHandler(openDialog)).Methods("POST")
-	api.BaseRoutes.APIRoot.Handle("/actions/dialogs/submit", api.APISessionRequired(submitDialog)).Methods("POST")
+	api.BaseRoutes.APIRoot.Handle("/actions/dialogs/open", api.APIHandler(openDialog)).Methods(http.MethodPost)
+	api.BaseRoutes.APIRoot.Handle("/actions/dialogs/submit", api.APISessionRequired(submitDialog)).Methods(http.MethodPost)
 }
 
 func doPostAction(c *Context, w http.ResponseWriter, r *http.Request) {