bug#74862: `tests/store-deduplication.scm` fails on Asahi Linux

[Lukas Navickas]

`copy-file/deduplicate, sparse files` tests fail on asahi linux.

i do not have adequate grounding on this topic, but i made a few empirical 
tests changing the inputs.

the original tests create a file in `/tmp`, and fail.
if instead the file is on disk, some(all?) tests pass.
if instead the inputs are changed from 2*4096 to 2*16834, some tests pass.

tmpfs on apple silicon has a block size of 16834. i'm guessing this corresponds 
to its RAM page size.

i'm inferring that this test has a hidden dependency: the block size of the 
underlying filesystem that contains the tested files. it may be desirable to 
account for this dependency.