fix: add "" case for user.name

Signed-off-by: Andrea Terzolo <[email protected]>

rules/falco-incubating_rules.yaml

@@ -769,7 +769,7 @@
 # https://github.com/draios/sysdig/issues/954). So in that case, allow
 # a setuid.
 - macro: known_user_in_container
-  condition: (container and not user.name in ("<NA>","N/A"))
+  condition: (container and not user.name in ("<NA>","N/A",""))
 
 # Add conditions to this macro (probably in a separate file,
 # overwriting this macro) to allow for specific combinations of