tst_http2: Fix flaky authentication test

The h2 server is running in a separate thread, so while the previous
test was finished and the server was deleted, it could still emit
and have a queued emission in-flight which would be picked up by
the next running test.

Pick-to: 6.2 6.1 5.15
Change-Id: I26b1bc711df7473032d6078f35f8aca37c40137e
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

tests/auto/network/access/http2/tst_http2.cpp

@@ -988,6 +988,7 @@ void tst_Http2::authenticationRequired_data()
 void tst_Http2::authenticationRequired()
 {
     clearHTTP2State();
+    serverPort = 0;
     QFETCH(const bool, responseHEADOnly);
     POSTResponseHEADOnly = responseHEADOnly;
 
@@ -1055,6 +1056,10 @@ void tst_Http2::authenticationRequired()
     QCOMPARE(isAuthenticated(reqAuthHeader), success);
     if (success)
         QCOMPARE(receivedBody, expectedBody);
+    // In the `!success` case we need to wait for the server to emit this or it might cause issues
+    // in the next test running after this. In the `success` case we anyway expect it to have been
+    // received.
+    QTRY_VERIFY(serverGotSettingsACK);
 }
 
 void tst_Http2::serverStarted(quint16 port)