Add a test run with torch with torch.set_default_dtype(torch.float64)

[ev-br]

To avoid things like gh-273.

[ev-br]

Actually,

$ export ARRAY_API_TESTS_SKIP_DTYPES=uint16,uint32,uint6
$ export ARRAY_API_TESTS_MODULE="exec('from array_api_compat import torch as xp; import torch; torch.set_default_dtype(torch.float64)')"
$ pytest array_api_tests -v --max-examples=1_000 -v --xfails-file ../array-api-compat/torch-xfails.txt --skips-file ../array-api-compat/torch-skips.txt

does not bring new failures apart from gh-273. So maybe it's a nice to have, not high-prio.