Bugfix: Pin cargo-xbuild to v0.6.5 in CI

[Inquisitor-201]

The CI pipeline recently started failing because cargo-xbuild v0.6.6 (and its dependencies) requires edition2024, which is not supported by our current nightly Rust toolchain (1.80.0).

This PR locks the version to v0.6.5 to restore CI stability while keeping the existing toolchain environment.

Related Error:
feature edition2024 is required but not stabilized in this version of Cargo

[li041]

Maybe cargo install cargo-xbuild is redundant. The built-in -Zbuild-std feature in Cargo's nightly channel now handles cross-compiling the sysroot (core, alloc, std) automatically, and I do not see any usage of cargo-xbuild in our repo.

[Inquisitor-201]

Maybe cargo install cargo-xbuild is redundant. The built-in -Zbuild-std feature in Cargo's nightly channel now handles cross-compiling the sysroot (core, alloc, std) automatically, and I do not see any usage of cargo-xbuild in our repo.

Thanks, I'll see if it works.