fix(ci/cd): pin cargo-lambda back to 1.8.1 temporarily

[jlizen]

📬 Issue #, if available:
n/a
✍️ Description of changes:

Fix for:
https://github.com/awslabs/aws-lambda-rust-runtime/actions/runs/14909766508/job/41880956336#step:7:36

Error: RustCargoLambdaBuilder:CargoLambdaBuild - Cargo Lambda failed: Error: × Failed to collect zig cc options

This is a known regression in cargo-lambda: cargo-lambda/cargo-lambda#856

Pinning back until it is fixed upstream.

🔏 By submitting this pull request

• [x ] I confirm that I've ran cargo +nightly fmt.
• [ x] I confirm that I've ran cargo clippy --fix.
• [ x] I confirm that I've made a best effort attempt to update all relevant documentation.
• [ x] I confirm that my contribution is made under the terms of the Apache 2.0 license.