tst_QSslSocket: don't use deprecated RSA api

OpenSSL 3.1.2 can be configured with no-deprecated option, in this
case test fails to build.

Pick-to: 6.6 6.5 6.2
Change-Id: Icaf457f55fb001b632922856dbe4bbb5bdba220e
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

tests/auto/network/ssl/qsslsocket/tst_qsslsocket.cpp

@@ -1312,6 +1312,7 @@ void tst_QSslSocket::privateKey()
 #if QT_CONFIG(openssl)
 void tst_QSslSocket::privateKeyOpaque()
 {
+#ifndef OPENSSL_NO_DEPRECATED_3_0
     if (!isTestingOpenSsl)
         QSKIP("The active TLS backend does not support private opaque keys");
 
@@ -1345,6 +1346,7 @@ void tst_QSslSocket::privateKeyOpaque()
     QFETCH_GLOBAL(bool, setProxy);
     if (setProxy && !socket->waitForEncrypted(10000))
         QSKIP("Skipping flaky test - See QTBUG-29941");
+#endif // OPENSSL_NO_DEPRECATED_3_0
 }
 #endif // Feature 'openssl'.