PHPCS 3.6.2 added a sniff for a PSR-12 rule which was previously not strictly checked: "No blank line after the opening brace of a class".

This fixes the newly flagged issues.

Previously, in Travis, when the same branch was pushed again and the "Auto cancellation" option on the "Settings" page had been turned on (as it was for most repos), any still running builds for the same branch would be stopped in favour of starting the build for the newly pushed version of the branch.

To enable this behaviour in GH Actions, a `concurrency` configuration needs to be added to each workflow for which this should applied to.

More than anything, this is a way to be kind to GitHub by not wasting resources which they so kindly provide to us for free.

Refs:
* https://github.blog/changelog/2021-04-19-github-actions-limit-workflow-run-or-job-concurrency/
* https://docs.github.com/en/actions/learn-github-actions/workflow-syntax-for-github-actions#concurrency

... as `E_ALL` does not always contain _all_ errors across PHP versions.

Ref: https://github.com/fabpot/local-php-security-checker/blob/main/CHANGELOG.md

The action used to install Composer packages and handle the caching has released a new major (and some follow-up patch releases), which means, the action reference needs to be updated to benefit from it.

Refs:
* https://github.com/ramsey/composer-install/releases/tag/2.0.0
* https://github.com/ramsey/composer-install/releases/tag/2.0.1
* https://github.com/ramsey/composer-install/releases/tag/2.0.2

Adding `--no-interaction` to "plain" Composer commands to potentially prevent CI hanging if, for whatever reason, interaction would be needed in the future.

Ref: https://github.com/actions/checkout/releases