GH Actions: version update for `ramsey/composer-install`

[jrfnl]

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