I think the problem is that the master is trying to relocate the "upgraded_scroll" shard back to
the node on which it was previously allocated, but to which it can't be allocated now due to the
shard lock being held because of an in-progress scroll. As the master keeps on retrying and
retrying (and indefinitely tries so because max_retries does not apply to relocations, it blocks
any other lower-prioritized task from completing, which leads to the rolling upgrade tests failing
(see #48395).
Closes#48395
790cfc8ad2