//distribution/... won't build with bzlmod

[nathaniel-brough]

The error we are getting is along the lines of.

 bazel build //... --config bzlmod
INFO: Invocation ID: df7a45a2-88ff-4475-a249-cfd22b6c1e99
ERROR: Analysis of target '//distribution:relnotes' failed; build aborted: no such package '@rules_pkg.0.5.1//private': The repository '@rules_pkg.0.5.1' could not be resolved: Repository '@rules_pkg.0.5.1' is not visible from repository '@'
INFO: Elapsed time: 6.814s
INFO: 0 processes.
FAILED: Build did NOT complete successfully (13 packages loaded, 41 targets configured)
    currently loading: @stardoc.0.5.0//stardoc ... (2 packages)
    Fetching https://bcr.bazel.build/bazel_registry.json

However we have added rules_pkg as a dep in MODULES.bazel and it seems to work fine from the normal WORKSPACE.