Many failures to create Persistent Storage since 6.4 after first boot partitioning failed with "Timed out for waiting the udev queue being empty"

Since the 6.4 release, we've received dozens of WhisperBack reports that contain "Timed out for waiting the udev queue being empty", while these were extremely rare before. The first few ones that I analyzed are all about first time partitioning failing. While in the (very few) occurrences of this error message before 6.4, it happened after udevadm settle in tpsd, much later, so this looks like a new problem entirely, and a very common one unfortunately. This is a special case of #20163 (closed) but since it's completely new, I think it's worth treating separately: chances are we can identify the cause of this recent regression independently.

+ SYSTEM_PARTITION_SIZE=8192M
+ log_begin_msg 'Updating partition table'
+ _log_msg 'Begin: %s ... ' 'Updating partition table'
+ '[' y '=' y ]
+ return
+ sgdisk --move-second-header --randomize-guids '--delete=1' '--new=1:0:+8192M' '--typecode=1:C12A7328-F81F-11D2-BA4B-00A0C93EC93B' '--change-name=1:Tails' /dev/sda
Warning: The kernel is still using the old partition table.
The new table will be used at the next reboot or after you
run partprobe(8) or kpartx(8)
The operation has completed successfully.
+ settle
+ sync
+ udevadm settle
Timed out for waiting the udev queue being empty.

Then:

• tails-block-device-info sees the system partition is 1.4GB.
• When trying to create a Persistent Storage, partition_table.call_create_partition_sync fails with udisks-error-quark: GDBus.Error:org.freedesktop.UDisks2.Error.Failed: Requested start for the new partition 1473249280 overlaps with existing partition /dev/sda1. (0)