FoxWander
Adventurer
This kind of magic-won't-solve-this-scenario crops up in several classic D&D modules, and it always seems like lazy design, to me. Designing and enforcing one and only one way to solve a challenge is usually considered bad design and poor game mastering.
To be fair, it IS only the "gate" itself that's anti-magicked- the stone around it is normal. When I ran through the Tomb years ago as part of Return to the Tomb of Horrors, we bypassed the gate by turning the stone around it to mud. We figured out that a magic ring might open it (because of the riddle) but weren't about to sacrifice anything- in fact, we made a point of stripping everything valuable out of the Tomb. (We, by chance, had two portable holes in the party. We pulled the silver and gold of the chests, got the gold couch from later on, and even the adamantine door of the throne room. It's anti-magicked as well, but again, set in normal stone.)