Currently the CI fails to compile zerocopy due to a rustc issue: rust-lang/rust#144168

As a temporary solution we should pin the rustc version to a known working commit and revert it once the issue is fixed.

Failed CI runs:

• https://github.com/RustPython/RustPython/actions/runs/16384359032/job/46301444119
• https://github.com/RustPython/RustPython/actions/runs/16386583040/job/46306948881