tests: Disable test_virtio_block_topology for aarch64

The test test_virtio_block_topology is flaky on aarch64, let's disable
it until we find the right way to fix it.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

tests/integration.rs

@@ -4997,6 +4997,7 @@ mod tests {
         }
 
         #[test]
+        #[cfg(target_arch = "x86_64")]
         fn test_virtio_block_topology() {
             let focal = UbuntuDiskConfig::new(FOCAL_IMAGE_NAME.to_string());
             let guest = Guest::new(Box::new(focal));