Add github-actions and buildkite formats

[dnephin]

Github actions supports grouping log lines.

Buildkite supports managing log output.

Gitlab CI supports collapsed sections.

Teamcity support: https://github.com/gotestyourself/gotestsum/issues/316#issuecomment-1611446932

These allow some log output to be collapsed (hidden), and expanded by clicking on an arrow. gotestsum could use these features to provide better output when tests on run on these systems.

See https://github.com/gotestyourself/gotestsum/issues/312#issuecomment-1488048968 for some discussion about a buildkite format, and #315 for a first draft of the github actions format.

Some options for these formats:

1. A format similar to the current testname format. Each test would be a group, and expanding the group would show the full output of the test. Currently only failed tests have output, but it wouldn't be too difficult to change to all tests having output hidden by the group.
2. A format similar to the current pkgname format. Each package would be a group, and expanding the group would show the full list of tests in that package, or maybe only the failed test output.