Fix typo in tools/webidl_binder.py. NFC (#22851)

tools/webidl_binder.py

@@ -696,7 +696,7 @@ def add_bounds_check_impl():
 # Compute the height in the inheritance tree of each node. Note that the order of interation
 # of `implements` is irrelevant.
 #
-# After one iteration of the loop, all ancestors of child are guaranteed to have a a larger
+# After one iteration of the loop, all ancestors of child are guaranteed to have a larger
 # height number than the child, and this is recursively true for each ancestor. If the height
 # of child is later increased, all its ancestors will be readjusted at that time to maintain
 # that invariant. Further, the height of a node never decreases. Therefore, when the loop