2.9.0

This release upgrades ocramius/proxy-manager to use composer-runtime-api:^2: this
means that you will need composer:^2 to install this version of ProxyManager.

In order to upgrade to composer v2, you can run composer self-update --2 on your
development or CI/CD system.

In addition to that, few notable improvements:

• the ocramius/package-versions dependency has been replaced by composer-runtime-api
• testing and static analysis have been noticeably improved, making it easier for others
  to contribute to the project.

Total issues resolved: 9

• 599: Add psalm's github workflow thanks to @malukenho
• 600: Fix documentation code samples thanks to @malukenho
• 601: Remove travis in favor of github workflow thanks to @malukenho
• 602: Replace travis and scrutinizer badges with github build status shield images and sheperd images thanks to @Ocramius
• 603: Introduce a build task that runs off a locked dependency set (composer.lock) thanks to @Ocramius
• 604: Enable automatic review for phpcs thanks to @malukenho
• 606: Run xulieta in CI thanks to @malukenho
• 616: Only run static analysis and CS checks on locked dependencies thanks to @Ocramius
• 619: #617 upgrade from ocramius/package-versions to composer-runtime-api:^2 thanks to @Ocramius