aconfig: fix workspace resolver warning

Fix the following warning:

  warning: virtual workspace defaulting to `resolver = "1"` despite one or more workspace members being on edition 2021 which implies `resolver = "2"`
  note: to keep the current resolver, specify `workspace.resolver = "1"` in the workspace root's manifest
  note: to use the edition 2021 resolver, specify `workspace.resolver = "2"` in the workspace root's manifest
  note: for more details see https://doc.rust-lang.org/cargo/reference/resolver.html#resolver-versions

Further info: https://doc.rust-lang.org/edition-guide/rust-2021/default-cargo-resolver.html

Bug: N/A
Test: cargo c # no warnings related to the resolver
Change-Id: I5ee546e4f2ba9e854026bf4baee380e89cf4a01b