PHP 8.0 - PHPCS tests - incompatibility with exussum12/coverage-checker

[htdat]

Summary

From https://github.com/Automattic/Edit-Flow/runs/2407816247?check_suite_focus=true

PHP Fatal error:  Array and string offset access syntax with curly braces is no longer supported in /home/runner/work/Edit-Flow/Edit-Flow/vendor/exussum12/coverage-checker/src/ArgParser.php on line 25

As mentioned in #638 (comment), this can be resolved by giving more version options for exussum12/coverage-checker like the following:

^0.11.2 || ^1.0.0