Clear timeout on git HTTP client

Starting with Node.js 20, the built-in Node.js HTTP client now has a default timeout of 5s (5000ms). The HTTP client in isomorphic-git and the git http plugin in Antora use the built-in Node.js HTTP client under the covers (via simple-get). Thus, by upgrading to Node.js 20, the git HTTP client in Antora inherits this setting. As a result, if the server does not response in 5s, the connection will be terminated.

This compatibility issue can be addressed by explicitly setting the timeout and keepAlive settings used in Node.js 18 and earlier so that all versions of Node.js behave the same.