chore(deps): update msrv to v1.68

[renovate]

This PR contains the following updates:

Package	Update	Change	Pending
rust	minor	1.67 -> 1.68	1.74 (+5)

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Release Notes

rust-lang/rust (rust)

v1.68

Compare Source

===========================

• Update the GitHub RSA host key bundled within Cargo.
  The key was rotated by GitHub
  on 2023-03-24 after the old one leaked.
• Mark the old GitHub RSA host key as revoked.
  This will prevent Cargo from accepting the leaked key even when trusted by
  the system.
• Add support for @revoked and a better error message for @cert-authority in Cargo's SSH host key verification

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