Fix docker-in-docker release builds

[michaelsproul]

We can't build releases currently due to an error:

https://github.com/sigp/lighthouse/actions/runs/13962535380/job/39086393139

This seems to be caused by cross trying and failing to install the latest version of Rust. Cross should not be doing this AFAICT:

• "Couldn't install toolchain" cross-rs/cross#1649
• cross run contains rustup output on stdout cross-rs/cross#1645

Until that Cross issue is solved, I think we have two workarounds available:

• Keep the runner image up to date with latest Rust so that updates are a no-op (going with this to save the v7.0.0-beta.4 release), or
• Build with RUSTUP_PERMIT_COPY_RENAME=true, which is a workaround I picked up from here: Invalid cross-device link (os error 18) when building inside pods rust-lang/rustup#2949.

[michaelsproul]

This is happening again due to the latest Rust release:

• https://github.com/sigp/lighthouse/actions/runs/14258067057/job/39964214663