[Examples] Mark nbody example as unsupported

The nbody example is flaky right now on Linux only and is showing up in
Mojo nightlies. Just mark it as unsupported for all of `system-linux` for
now until we have time to dig into it more to unblock Mojo nightlies.

MODULAR_ORIG_COMMIT_REV_ID: 98ff9dfb5dd02267247af7f489fb5b5aaa23a972

examples/nbody.mojo

@@ -10,8 +10,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 # ===----------------------------------------------------------------------=== #
-# UNSUPPORTED: target-aarch64
-# COM: currently flaky on Linux only
+# UNSUPPORTED: system-linux
+# COM: currently flaky on Linux only, see SDLC-1080
 # RUN: %mojo %s
 
 # This sample implements the nbody benchmarking in