fix: Revert "bug: GreyNoise last_seen attribute had been referenced b…

…y a non-extant field name. update to an extant field (#486)" (#496)

This reverts commit f86b06b.

global_helpers/panther_greynoise_helpers.py

@@ -102,7 +102,7 @@ def first_seen(self, match_field) -> datetime.date:
         return parser.parse(deep_get(self.noise, match_field, "first_seen"))
 
     def last_seen(self, match_field) -> datetime.date:
-        return parser.parse(deep_get(self.noise, match_field, "last_seen"))
+        return parser.parse(deep_get(self.noise, match_field, "last_seen_timestamp"))
 
     def asn(self, match_field) -> str:
         return deep_get(self.noise, match_field, "metadata", "asn")