build-configs.yaml: upgrade rust-for-linux_rust to rustc-1.66

The `rust` branch of `rust-for-linux` is moving to Rust 1.66.0 [1],
therefore, use the new build environment for it.

Link: Rust-for-Linux/linux#947 [1]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

config/core/build-configs.yaml

@@ -1106,8 +1106,8 @@ build_configs:
     tree: rust-for-linux
     branch: 'rust'
     variants:
-      rustc-1.62:
-        build_environment: rustc-1.62
+      rustc-1.66:
+        build_environment: rustc-1.66
         fragments: [rust, rust-for-linux-samples, kselftest]
         architectures:
           x86_64: