README.md: fix travis badge (ethereum#28889)

The hyperlink in the README file that directs to the Travis CI build was broken.
This commit updates the link to point to the corrent build page.

README.md

@@ -6,7 +6,7 @@ Golang execution layer implementation of the Ethereum protocol.
 https://pkg.go.dev/badge/github.com/ethereum/go-ethereum
 )](https://pkg.go.dev/github.com/ethereum/go-ethereum?tab=doc)
 [![Go Report Card](https://goreportcard.com/badge/github.com/ethereum/go-ethereum)](https://goreportcard.com/report/github.com/ethereum/go-ethereum)
-[![Travis](https://travis-ci.com/ethereum/go-ethereum.svg?branch=master)](https://travis-ci.com/ethereum/go-ethereum)
+[![Travis](https://app.travis-ci.com/ethereum/go-ethereum.svg?branch=master)](https://app.travis-ci.com/github/ethereum/go-ethereum)
 [![Discord](https://img.shields.io/badge/discord-join%20chat-blue.svg)](https://discord.gg/nthXNEv)
 
 Automated builds are available for stable releases and the unstable master branch. Binary