Tincan error in the `set_error_handler` method due to incompatibility with PHP 8.0

[GrahamStaveleyBerry]

As of PHP 8.0, the native PHP method set_error_handler now only accepts 4 parameters instead of 5 due to the variable $errcontext being removed.

See PHP official Docs:
https://www.php.net/manual/en/function.set-error-handler.php

Warning
This parameter has been DEPRECATED as of PHP 7.2.0, and REMOVED as of PHP 8.0.0. If the function defines this parameter without a default, an error of "too few arguments" will be raised when it is called.

### Tasks

[jonathan-bird]

Would be great if someone could merge this