Unnecessary "Splicing Cargo workspace for `crates`" under Bazel 9

[rejuvenile]

Under Bazel 9, back to back no-op builds will sometimes take an extra 30 seconds due to:

Fetching module extension @@rules_rust+//crate_universe:extensions.bzl%crate; Splicing Cargo workspace for crates 8s

... which seems unnecessary in a back to back no-op build.