Fix `ExtendedOpcode::MAX` for Pulley (#12867)

This was off-by-one which could lead to possible undefined behavior in
Miri and at runtime when disassembling invalid opcodes. This isn't
reachable from

Fix `ExtendedOpcode::MAX` for Pulley (#12867)

This was off-by-one which could lead to possible undefined behavior in
Miri and at runtime when disassembling invalid opcodes. This isn't
reachable from Wasmtime itself since Cranelift only generates valid
opcodes, but it's nonetheless reachable via `wasmtime objdump` and still
good to fix.

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