Use union type expression in ExpressionTokenizer.equal

Other places already use this syntax so use it to be consistent.

Co-authored-by: Erik Schamper <[email protected]>

dissect/cstruct/expression.py

@@ -18,7 +18,7 @@ def __init__(self, expression: str):
         self.pos = 0
         self.tokens = []
 
-    def equal(self, token: str, expected: Union[str, set[str]]) -> bool:
+    def equal(self, token: str, expected: str | set[str]) -> bool:
         if isinstance(expected, set):
             return token in expected
         else: