SFSToSIFSStore migration updates index with wrong segment

While fixing compaction bugs with SIFS a test failure started appearing. This was caused due to SFSToSIFS migration not updating the index properly. An explanation is at https://github.com/infinispan/infinispan/pull/11338#issuecomment-1753357309. Interestingly the test does not fail in prior versions despite the index being the wrong segment, so it may not be seen by customers. The easiest workaround is just to delete the SIFS index directory after migration and it will rebuild the index properly.