devel/rubygem-opentelemetry-instrumentation-action_mailer: Update to 0.8.0

• Take maintainership

Changes: https://github.com/open-telemetry/opentelemetry-ruby-contrib/releases

		https://github.com/open-telemetry/opentelemetry-ruby-contrib/blob/main/instrumentation/action_mailer/CHANGELOG.md

Approved by: mfechner (maintainer, via private email)