message: Fix the build by avoiding bitvec 0.18.5.
  bitvec 0.18.5 pulls in radium 0.3.0, which does not support platforms without atomics. Pulling in bitvec 0.18.4 brings in radium 0.4 instead (was there a bug in 0.4?) which restores our build.
diff: @@ -26,7 +26,11 @@ corepack = { version = "0.4.0", default-features = false, features = ["alloc"] }
  # with the nightly toolchain used by libtock-rs.
  serde = { version = "=1.0.114", default-features = false, features = ["derive"] }
  ctap2-authenticator = { git = "https://gitlab.com/ctap2-authenticator/ctap2-authenticator.git" }
  -p256 = { version = "0.5.0" , default-features = false, features = ["arithmetic", "ecdsa", "ecdsa-core"] }
  +p256 = { version = "0.7" , default-features = false, features = ["arithmetic", "ecdsa", "ecdsa-core"] }
  +# p256 depends transitively on bitvec 0.18. bitvec 0.18.5 depends on radium
  +# 0.3.0, which does not work on platforms that lack atomics. This prevents cargo
  +# from selecting bitvec 0.18.5, which avoids the radium 0.3.0 issue.
  +bitvec = { version = "<=0.18.4", default-features = false }
  subtle = { version = "2.3.0", default-features = false, features = ["i128"] }
  generic-array = { version = "0.14.3" }
  libmctp = { version = "0.1.0" }
  