test: fix WASI link test

The WASI link test attempts to create a link in the temporary directory
to a file in the fixtures directory and can fail if those directories
are on different devices. Update the test so that both the source and
target of the link reside on the same device.

PR-URL: https://github.com/nodejs/node/pull/39485
Fixes: https://github.com/nodejs/node/issues/39484


Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>