Rust 1.75

[ojeda]

This time around, keep rustc-1.74 around, since we will use both (i.e. the latest and the previous latest).

Needs testing in staging first, please see https://github.com/kernelci/kernelci-deploy/pull/121.

Upgrade PRs:

• https://github.com/kernelci/kernelci-core/pull/2321.
• https://github.com/kernelci/kernelci-deploy/pull/121.
• https://github.com/kernelci/kernelci-deploy/pull/122.

[nuclearcat]

Tested on staging, docker repos created