doc: add versionadded to ExceptionInfo.group_contains

[bastimeyer]

ExceptionInfo.group_contains() was added in 8.0.0 (via #11424) and currently lacks the versionadded data in pytest's docs:

• https://docs.pytest.org/en/8.0.x/reference/reference.html#pytest.ExceptionInfo.group_contains
• https://docs.pytest.org/en/latest/reference/reference.html#pytest.ExceptionInfo.group_contains

[nicoddemus]

Awesome, thanks!