Set a descriptive User Agent for requests, so sourceforge.net does not complain.

src/modules/netinstall/NetInstallPage.cpp

@@ -155,6 +155,9 @@ void NetInstallPage::loadGroupList()
     request.setUrl( QUrl( confUrl ) );
     // Follows all redirects except unsafe ones (https to http).
     request.setAttribute(QNetworkRequest::FollowRedirectsAttribute, true);
+    // Not everybody likes the default User Agent used by this class (looking at you,
+    // sourceforge.net), so let's set a more descriptive one.
+    request.setRawHeader( "User-Agent", "Mozilla/5.0 (compatible; Calamares)" );
 
     connect(&m_networkManager, &QNetworkAccessManager::finished,
             this, &NetInstallPage::dataIsHere);