Update anaconda additional repository flow

"Additional repositories" is now hidden behind a dropdown we
have to open first. This will make the test fail on anything
older than Fedora-Rawhide-20230121.n.0, but I don't think we
run this test anywhere that would be a problem.

Signed-off-by: Adam Williamson <awilliam@redhat.com>

needles/anaconda/install_source/add_dropdown-20230123.json

@@ -0,0 +1,15 @@
+{
+  "area": [
+    {
+      "height": 19,
+      "type": "match",
+      "ypos": 386,
+      "width": 81,
+      "xpos": 26
+    }
+  ],
+  "properties": [],
+  "tags": [
+    "anaconda_add_dropdown"
+  ]
+}

tests/install_source_graphical.pm

@@ -59,6 +59,7 @@ sub add_repo {
         $repourl =~ s/^ml://;
     }
     # configure an additional repository
+    assert_and_click "anaconda_add_dropdown";
     assert_and_click "anaconda_add";
     # shift-tab seven times gets us to the scheme box
     for (my $i = 0; $i < 7; $i++) {