Cython language_level was set to 3 in v13.1.0, but code still contains Python 2 syntax #1749

My code went into an infinite loop throwing exceptions after upgrading from v12.2.0, and I managed to find the offending code after trying every subsequent version.

I've found that Cython language_level was set to 3 in 0a7e549, but av/error.pyx still uses Python 2 syntax here, resulting in the same exception being thrown over and over again.