fix[test]: add missing keywords to reserved list (#4763)

fixes fuzz failure in `test_call_graph_stability.py` which relies on
`RESERVED_KEYWORDS` to filter invalid programs.

Author: Sporarum

vyper/ast/identifiers.py

@@ -64,6 +64,8 @@ def validate_identifier(attr, ast_node=None):
     "internal",
     "payable",
     "nonreentrant",
+    "staticcall",
+    "extcall",
     # "class" keywords
     "interface",
     "struct",