As of [Forgejo runner 5.0.1](5889426664), RUNNER_TOOL_CACHE is set but it is not pre-populated. By default it does not exist but a dedicated container image my place shared tools at that location for actions / workflows that expect them to be advertised by this environment variable.
Resolvesforgejo/runner#901
Reviewed-on: https://code.forgejo.org/forgejo/end-to-end/pulls/968
Co-authored-by: Earl Warren <contact@earl-warren.org>
Co-committed-by: Earl Warren <contact@earl-warren.org>