Release/v6.30.0 (#857)

* remove copy buildkite command from dockerfile.ruby-maze-runner

* add ruby4.0 to unit tests

* Update CI, gemfile and logger spec for compatibility with all supported Ruby versions

* remove trailing whitespaces

* Use shell string for ruby 1.9.x to ensure compatibility

* suggestion-add timeout,remove name params from method,change Gemfile to spec fixture for compatibility and changelog entry

* update condition for modern bundler version support with simple approach

* moved ostruct gem to test group and remove changelog entry as only updating unit tests/fixtures

* Switch to ActiveSupport::Notifications.monotonic_subscribe

* monotonic_subscribe was introduced in Rails 6.1+, add condition accordingly

* change entry in CHANGELOG

* Release v6.30.0

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Co-authored-by: Steve Kirkland <twometresteve@users.noreply.github.com>
Co-authored-by: Adam Renberg Tamm <adam.renbergtamm@shopify.com>

Merge pull request #852 from bugsnag/release/v6.29.0

Release v6.29.0

Merge pull request #841 from bugsnag/release/v6.28.0

Release v6.28.0

Release v6.27.1

Release v6.27.0

Release v6.26.4

Release v6.26.3

Release v6.26.2

Release v6.26.1

Release v6.26.0