Add SEPARATE_WORKSPACE requirement for run_tests
Add SEPARATE_WORKSPACE requirement for run_tests

The io_uring and fuzz crate cannot be tested in the same workspace
via `cargo test -p io_uring -p fuzz`.
This change allows test_runner.py to run tests independently by
cd'ing into the crates directory and running cargo test in there.

BUG=b:181672910
BUG=b:181673923
TEST=Tests for the above mentioned crates can be enabled and run, but
test failures prevent them from being enabled so far.

Change-Id: Ia03868d53e508549fe2f071da399b982359a8834
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2749772
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Commit-Queue: Dennis Kempin <cd09796fb571bec2782819dbfd33307f65b1c778@google.com>

google/crosvm,google/crosvm,google/crosvm,google/crosvm