fix: bad assertion in expr.py (#3758)

in addition to structs and interfaces, some builtins can also be skipped
by the constant folder.

tests/functional/syntax/test_constants.py

@@ -279,6 +279,13 @@ def deposit(deposit_input: Bytes[2048]):
 CONST_BAR: constant(Foo) = Foo({a: 1, b: 2})
     """,
     """
+CONST_EMPTY: constant(bytes32) = empty(bytes32)
+
+@internal
+def foo() -> bytes32:
+    return CONST_EMPTY
+    """,
+    """
 struct Foo:
     a: uint256
     b: uint256

vyper/codegen/expr.py

@@ -190,9 +190,6 @@ def parse_Name(self):
             varinfo = self.context.globals[self.expr.id]
 
             if varinfo.is_constant:
-                # constants other than structs and interfaces should have already gotten
-                # propagated during constant folding
-                assert isinstance(varinfo.typ, (InterfaceT, StructT))
                 return Expr.parse_value_expr(varinfo.decl_node.value, self.context)
 
             assert varinfo.is_immutable, "not an immutable!"