Update github action shield link. (#2738)

Author: nojaf

README.md

@@ -3,7 +3,7 @@ Fantomas
 
 ![Fantomas logo](https://raw.githubusercontent.com/fsprojects/fantomas/main/fantomas_logo.png)
 
-![GitHub Workflow Status (event)](https://img.shields.io/github/workflow/status/fsprojects/fantomas/Build%20main?event=push&label=Build%20main&style=flat-square)
+![GitHub Workflow Status (event)](https://img.shields.io/github/actions/workflow/status/fsprojects/fantomas/main.yml?branch=main&label=Build%20main&style=flat-square)
 [![Discord](https://img.shields.io/discord/940511234179096586?label=Fantomas%20Discord&style=flat-square)](https://discord.gg/D5QXvQrBVa)
 [![Nuget (with prereleases)](https://img.shields.io/nuget/vpre/fantomas?style=flat-square)](https://www.nuget.org/packages/fantomas/absoluteLatest)