Skip test_file_shortcut on Linux under CI

This test fails like similar tests in the same file because there
is no proper X server.

spyder/plugins/editor/widgets/editorstack/tests/test_shortcuts.py

@@ -372,6 +372,11 @@ def test_shortcuts_for_new_editors(editorstack, qtbot):
     qtbot.keyClick(editor, Qt.Key_1, modifier=Qt.ControlModifier)
     assert editor.toPlainText() == '# Line5\nLine6\nLine7\nLine8\n'
 
+
+@pytest.mark.skipif(
+    sys.platform.startswith('linux') and running_in_ci(),
+    reason="It fails on Linux due to the lack of a proper X server."
+)
 @pytest.mark.parametrize(
     'key, modifier, action',
     [