We should not update a version from the repo is not in sources

[mauritsvanrees]

I just noticed that in Plone 6.1.4 I have accidentally included plone.app.drafts 3.0.0, with native namespaces. See https://community.plone.org/t/plone-6-1-4-released/22769/5

Fixed in plone/buildout.coredev@0623856

I think plone.releaser did this while I was making a plone.app.drafts release for 6.2. And it updated the pin in the coredev 6.1 branch without checking if the 6.1 sources have the same branch as 6.2. Well, that check is probably done, but the code draws the wrong conclusion when the repo is not in the sources list at all.
I have added it now.