Add `roave/backward-compatibility-check` checks during tests

[Marco Pivetta]

[James Titcumb]

Adding,...

[James Titcumb]

Hmm, upstream dependency issue?

$ composer require --update-with-all-dependencies --dev roave/backward-compatibility-check
Using version ^4.2 for roave/backward-compatibility-check
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Can only install one of: phpdocumentor/type-resolver[1.0.1, 0.4.0].
    - Can only install one of: phpdocumentor/type-resolver[0.4.0, 1.0.1].
    - Can only install one of: phpdocumentor/type-resolver[0.4.0, 1.0.1].
    - roave/better-reflection 3.5.0 requires phpdocumentor/type-resolver ^0.4.0 -> satisfiable by phpdocumentor/type-resolver[0.4.0].
    - roave/backward-compatibility-check 4.2.0 requires roave/better-reflection ^3.5.0 -> satisfiable by roave/better-reflection[3.5.0].
    - Installation request for roave/backward-compatibility-check ^4.2 -> satisfiable by roave/backward-compatibility-check[4.2.0].
    - Installation request for phpdocumentor/type-resolver (locked at 1.0.1) -> satisfiable by phpdocumentor/type-resolver[1.0.1].


Installation failed, reverting ./composer.json to its original content.

[Marco Pivetta]

It doesn't necessarily need to land in the same directory as this project, since it doesn't integrate with the sources