cargo vendor outputs a TOML config block to stdout with [source.*]
overrides matching the actual git revisions / source IDs of vendored
deps (including ?rev=... keys for git-pinned dependencies). This output
was previously discarded, leaving package authors to maintain
.gear/config.toml manually — which silently goes stale when upstream
updates a git rev pin and breaks offline builds.

Now rpmgs redirects the stdout to $RGD/.gear/config.toml during
update_predownloaded() and stages it alongside the vendor commit, so
the source override always matches the vendored crates.