Fixes #35120 where dragging patterns multiple times will insert blocks with duplicate clientIds. This isn't a problem for onClick since we explicitly clone the blocks in that case.

If we don't like the code approach here, one alternative is always cloning for the 'inserter' case since we never intend to add duplicate clientIds. (It happens to work for the inserter drag currently since it re-renders that often).

Step-by-step reproduction instructions

1. In the post-editor try adding a pattern via drag
2. Add the same pattern again
3. Check the clientIds assigned using wp.data.select('core/block-editor').getBlocks()

Before:

After: