linux_testing: fix Rust support with current rustc

This won't build at present, because a fix for the rustc wrapper needs
to go through staging.

+1
+1
pkgs/top-level/linux-kernels.nix
··· 203 203 kernelPatches = [ 204 204 kernelPatches.bridge_stp_helper 205 205 kernelPatches.request_key_helper 206 + kernelPatches.rust_1_75 206 207 ]; 207 208 }; 208 209 latest = packageAliases.linux_latest.kernel;