Generate temporary Gemfile.lock for FOSSA CI scan

[kaylareopelle]

FOSSA scans expect a Gemfile.lock to do their work. Gems, as a best practice, do not check in a Gemfile.lock.

The New Relic Ruby agent gets around this by bundling the gem in a step prior to the scan:
https://github.com/newrelic/newrelic-ruby-agent/actions/runs/14669694175/workflow

Something similar may work for this repo, though we'll need to adjust so that all the nested gems get bundled.

Until then, FOSSA scans will fail.

Example: https://github.com/open-telemetry/opentelemetry-ruby-contrib/actions/runs/14674537659

[github-actions]

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[kaylareopelle]

Scans are silently failing. When you open the action, you'll see the failures, but the scan itself will pass.