Enhance routers for the Actions variable operations (#33547)

- Find the variable before updating or deleting
- Move the main logic from `routers/web/repo/setting/variables.go` to
`routers/web/shared/actions/variables.go`.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

routers/api/v1/org/action.go

@@ -450,7 +450,11 @@ func (Action) UpdateVariable(ctx *context.APIContext) {
 	if opt.Name == "" {
 		opt.Name = ctx.PathParam("variablename")
 	}
-	if _, err := actions_service.UpdateVariable(ctx, v.ID, opt.Name, opt.Value); err != nil {
+
+	v.Name = opt.Name
+	v.Data = opt.Value
+
+	if _, err := actions_service.UpdateVariableNameData(ctx, v); err != nil {
 		if errors.Is(err, util.ErrInvalidArgument) {
 			ctx.Error(http.StatusBadRequest, "UpdateVariable", err)
 		} else {