gh-92886: [clinic.py] raise exception on invalid input instead of assertion (GH-98051)

Tests should pass with -O (assertions off).

Automerge-Triggered-By: GH:iritkatriel

Tools/clinic/clinic.py

@@ -495,7 +495,8 @@ def permute_optional_groups(left, required, right):
     result = []
 
     if not required:
-        assert not left
+        if left:
+            raise ValueError("required is empty but left is not")
 
     accumulator = []
     counts = set()