CMakeLists: disable Seastar_IO_URING to fix seastar unittest timeout

CMakeLists: disable Seastar_IO_URING to fix seastar unittest timeout

As pr https://github.com/ceph/ceph/pull/55787 bump liburing from 0.7 to 2.5.
with liburing-dev (2.1) installed on ubuntu jammy, Seastar_IO_URING will be set ON,
seastar will be builded with liburing-dev. Ceph bluestore use build_uring in file Builduring.cmake
to build liburing version 2.5 and set URING_INCLUDE_DIR to
/home/jenkins-build/build/workspace/ceph-pull-requests/build/src/liburing/src/include/liburing/,
seastar use URING_INCLUDE_DIR(version is 2.5) to build, but seastar link liburing.so to system
liburing-dev package(version 2.1). The liburing head file seastar building and liburing binary
seastar linked is mismatched.
I have downgraded the liburing version in file 'cmake/modules/Builduring.cmake' to liburing-2.1,
the seastar unittests work fine, no timeout.

Fixes: https://tracker.ceph.com/issues/64789
Signed-off-by: luo rixin <luorixin@huawei.com>