Update magic constant for unordered_map_killer

[imsuck]

Previous magic constant generated from ideone is only for C++14 (and below?). I have updated it to a new constant which would work from C++17 to C++23. Checked the constant locally, through Library Checker's hacks and on onlinegdb.

Resolves #1338.

[maspypy]

I really appreciate it.
However, it would be helpful if you could address it by adding new test cases rather than modifying the existing ones. In general, we do not delete existing test cases.

One approach is:
int MAGIC = vector({256279, 218971, 205759, 172933})[seed % 4];
and setting the number of test cases to 4 by editing info.toml.

[maspypy]

thank you!