Reducing a suspension to a silence doesn't un-suspend users

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Steps to reproduce the problem

1. Create an instance block of type suspend
2. Observe that all known users of that instance are now suspended
3. Edit the domain block to change the type to silence
4. Observe that users on that instance are still suspended, not silenced.

Expected behaviour

Users are silenced, not suspended, when the instance block type is changed

Actual behaviour

Users remain suspended

Detailed description

Reported in https://glitterkitten.co.uk/@doot/109473559996024287, confirmed locally.

Removing the domain block from a suspended domain entirely unblocks users as expected, but editing to change it to a silence leaves the individual users all blocked.

Specifications

Mastodon 4.0.2