fix: update soroban deps to prerelease

[willemneal]

When testing out the procotol22 branch with quickstart, I got an XDR length error, which suggests that this is perhaps out of date with the xdr of the env. So I updated here. However, I'm getting the following error.

error: failed to select a version for k256.
    ... required by package soroban-env-host v22.0.0-rc.2
    ... which satisfies dependency soroban-env-host-curr = "=22.0.0-rc.2" of package preflight v21.4.0 (/Users/willem/c/s/soroban-rpc/cmd/soroban-rpc/lib/preflight)
versions that meet the requirements ^0.13.3 are: 0.13.4, 0.13.3
all possible versions conflict with previously selected packages.
  previously selected package k256 v0.13.1
    ... which satisfies dependency k256 = "=0.13.1" of package soroban-env-host v21.2.0
    ... which satisfies dependency soroban-env-host-prev = "=21.2.0" of package preflight v21.4.0 (/Users/willem/c/s/soroban-rpc/cmd/soroban-rpc/lib/preflight)

[willemneal]

@graydon Is it possible to upgrade k256 in the earlier version of the env-host? If not, how do I get around this? I tried using patch and adding k256 to the workspace and crate. Nevermind just saw #316

[willemneal]

In favor of #316