Latest version requires php 8.0 functionality

[tsdogs]

Updating to latest version on debian 11 with php 7.4 raised an error about function str_constrains() not found. It's a function introduced in php 8.0

The composer.json should be changed accordingly or require the package symfony/polyfill-php80 which implements it. I have solved installing symfony/polyfill-php80

It was introduced with Pull Request #88