Connection error when downloading manifest is not properly handled

If there is a connection error when downloading the manifest, the code continues on as if there was no error rather than rethrowing it. As a result, the user sees the resulting fault:

../node_modules/@antora/atlas-extension/lib/read-site-manifest.js:49
              if (response.statusCode !== 200) {
                           ^
TypeError: Cannot read properties of undefined (reading 'statusCode')

The problem is that the get handler does not return after rejecting the promise.