Re-configure infection to push mutation score reports for all stable branches

[Ocramius]

See https://github.com/psr7-sessions/storageless/runs/3742041520?check_suite_focus=true#step:8:56, which reports:

Warning:  Dashboard report has not been sent: Branch "8.3.x" does not match expected badge configuration

This has been made configurable in infection/infection#1538, and released in https://github.com/infection/infection/releases/tag/0.24.0

We'll need to adjust some configuration for it to work properly with the new branch naming mechanism :-)

[Ocramius]

Badge will likely never work, because the branch name constantly changes 🤔

[lcobucci]

Badge will likely never work, because the branch name constantly changes 🤔

I reckon we can use a regex.. something like /\d\.\d\.x/ should suffice, the tricky bit is keeping README up to date.

[Ocramius]

IMO worth having this as badge feature request instead 😬

[Ocramius]

Handled in 57bb1df