packagevariant controller should unpropose deletion when needed

[natasha41575]

Ran into this scenario when playing around with the packagevariant controller:

• I create a PackageVariant with a target downstream package foo. The PackageVariant controller creates the target draft package revision, and I publish it, resulting in foo v1.
• I update the PackageVariant's target downstream package name to something else, like bar. The PackageVariant controller creates a new target draft package revision bar. It also sees that it owns a package revision foo v1 that no longer matches its target, so proposes foo v1 for deletion. This is working great so far.
• I update the PackageVariant's target downstream package name back to foo. The PackageVariant controller deletes its package revision bar. The controller also sees that there is already a package revision foo v1 that it owns that matches its target, so it does nothing -- meaning that foo v1 stays proposed for deletion. This PR makes it so that in such a case, the target package revision's lifecycle gets changed back from DeletionProposed to Published.