qtest/virtio-9p-test.c: remove g_test_slow() gate

qtest/virtio-9p-test.c: remove g_test_slow() gate

Commit 558f5c42ef gated the local tests with g_test_slow() to skip them
in 'make check'. The reported issue back then was this following CI
problem:

https://lists.nongnu.org/archive/html/qemu-devel/2020-11/msg05510.html

This problem ended up being fixed after it was detected with the
recently added risc-v machine nodes [1]. virtio-9p-test.c is now
creating and removing temporary dirs for each test run, instead of
creating a single dir for the entire qos-test scope.

We're now able to run these tests with 'make check' in the CI, so let's
go ahead and re-enable them.

This reverts commit 558f5c42efded3e0d0b20a90bce2a9a14580d824.

[1] https://mail.gnu.org/archive/html/qemu-devel/2024-03/msg05807.html

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-Id: <20240327142011.805728-3-dbarboza@ventanamicro.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Tested-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>