Fix workflow link (#372)

Noticed this filename didn't match in the README.

Signed-off-by: Stefan VanBuren <svanburen@buf.build>

Author: stefanvanburen

README.md

@@ -1,7 +1,7 @@
 Connect-Swift
 =============
 
-[![Build](https://github.com/connectrpc/connect-swift/actions/workflows/ci.yaml/badge.svg?branch=main)](https://github.com/connectrpc/connect-swift/actions/workflows/ci.yaml)
+[![Build](https://github.com/connectrpc/connect-swift/actions/workflows/ci.yml/badge.svg?branch=main)](https://github.com/connectrpc/connect-swift/actions/workflows/ci.yml)
 [![Version](https://img.shields.io/cocoapods/v/Connect-Swift.svg?style=flat)](https://cocoapods.org/pods/Connect-Swift)
 [![Platform](https://img.shields.io/cocoapods/p/Connect-Swift.svg?style=flat)](https://cocoapods.org/pods/Connect-Swift)
 [![License](https://img.shields.io/cocoapods/l/Connect-Swift.svg?style=flat)](https://cocoapods.org/pods/Connect-Swift)