tests: exclude test_fw_cfg for mshv

test_fw_cfg is frequently failing in the CI for MSHV. Exclude it for
now. It needs further investigation. See issue #7434 for details.

Signed-off-by: Anirudh Rayabharam <anrayabh@microsoft.com>

tests/integration.rs

@@ -11687,6 +11687,7 @@ mod fw_cfg {
     use crate::*;
 
     #[test]
+    #[cfg_attr(feature = "mshv", ignore = "See #7434")]
     fn test_fw_cfg() {
         let disk_config = UbuntuDiskConfig::new(JAMMY_IMAGE_NAME.to_string());
         let guest = Guest::new(Box::new(disk_config));