nogo: exclude_files requires hardcoding external bzlmod paths

Before bzlmod the config would have simple `external/` entries. With bzlmod these would require the full path, e.g. `external/gazelle~~go_deps~`. This would be bad practice as these path are not stable.

Review the existing nogo exclude_files configuration and its behavior under bzlmod, using the external/ and external/gazelle~~go_deps~ examples. Confirm the expected stable path form and verify that dependencies can be excluded without hardcoding unstable bzlmod paths.

Written by the indexing model from the issue text.