Gerrit should not create new patch-sets when staging

It's very painful for integrators like me.

• https://codereview.qt-project.org/c/qt/qt5/+/265866 Merge remote-tracking branch 'origin/5.12.4' into 5.12
• https://codereview.qt-project.org/c/qt/qt5/+/265403/ platform_configs: Add missing "Configure arguments" to qtconnectivity.txt
• https://codereview.qt-project.org/c/qt/qt5/+/266027/ Update submodules on '5.12' in qt5

I want to have them in order(from up to down), but after first stage and fail. Their patch set numbers got bumped.

When I tried to get new round of submodule update which based on previous "-fetch-ref" which I used latest patch set number, refs/changes/03/265403/3, then got failure

To ssh://codereview.qt-project.org:29418/qt/qt5
 ! [remote rejected]     5ca756ff68f0517ee77e138d00b4b94f286ae211 -> refs/for/5.12 (commit aaf43ef: you are not allowed to upload merges)
error: failed to push some refs to 'ssh://qt_submodule_update_bot@codereview.qt-project.org:29418/qt/qt5'

If I use previous patch set number, for example, refs/changes/03/265403/1, supermodule update script works fine. But when staging in gerrit, I got merge conflict there.