Update dependencies

[pavog]

composer audit reported security advisories for the locked versions of guzzlehttp/guzzle, guzzlehttp/psr7 and phpunit/phpunit.

• allow guzzlehttp/guzzle 8 and guzzlehttp/psr7 3, the lock file now uses guzzle 8.2.0 and psr7 3.1.0
• keep supporting guzzle 7 and psr7 2, but raise the minimum versions to ^7.15.2, ^2.12.3
• update phpunit to 12.5.39