Update README

Author: JannikLassahn

README.md

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 # graphql-dotnet-upload
 
-[![Build Status](https://dev.azure.com/lassahn/graphql-dotnet-upload/_apis/build/status/JannikLassahn.graphql-dotnet-upload?branchName=master)](https://dev.azure.com/lassahn/graphql-dotnet-upload/_build/latest?definitionId=1&branchName=master)
+[![Build Status](https://github.com/JannikLassahn/graphql-dotnet-upload/actions/workflows/ci.yml/badge.svg)](https://github.com/JannikLassahn/graphql-dotnet-upload/actions/workflows/ci.yml)
 [![NuGet](https://img.shields.io/nuget/v/GraphQL.Upload.AspNetCore.svg?style=flat)](https://www.nuget.org/packages/GraphQL.Upload.AspNetCore/)
 
 This repository contains an experimental implementation of the [GraphQL multipart request spec](https://github.com/jaydenseric/graphql-multipart-request-spec) based on ASP.NET Core.