test: fix integration tests relying on specific byte amounts

The integration tests for the volume resize feature rely on specific byte
amounts that a ext4 filesystem on a fake block device has. The specific
amounts recently changed, probably through a new version of mkfs.ext4.

This amount equals the values from our GitHub Actions pipeline, as well
as my local machine.

The amounts might need to be changed again in the future if the tests start
failing again, we might consider removing tests for the specific amounts,
and just check that the resized number is larger than the initial if this
happens often.