Bump parity-scale-codec to 2.2.0-rc.1

[Xanewok]

Part of paritytech/substrate#9163.

This is a pre-release so that we can experiment a bit more with the MaxEncodedLen trait if needed, but since Cargo wants pre-releases to be explicitly specified (and are not considered automatically SemVer-compatible), this does exactly that. That's also needed so that we can select a single parity-scale-codec version in the Substrate crate graph.

[ordian]

There is a general argument whether you need to release a version of lib that just bumps a semver-compatible version of a dep. I don't mind doing it, but I don't think it's required in this case.

[Xanewok]

As mentioned in the OP:

Cargo wants pre-releases to be explicitly specified (and are not considered automatically SemVer-compatible)

this means that 2.2.0-rc.1 is not compatible with 2.0.0 because of the pre-release part being added, so we need to explicitly upgrade it here.

Technically we could wait until we're satisfied with the RCs and release a full 2.2.0 and so we wouldn't need to do anything here but AIUI we want more freedom in changing how the newly added MaxEncodedLen works as we progress with PoV benchmarks in Substrate.