chore(ubi-rust-builder): Bump Rust toolchain to 1.81.0

[NickLarsenNZ]

Description

Part of stackabletech/operator-rs#898

Bump the ubiX rust-biulder images to Rust 1.81.0.

Definition of Done Checklist

• Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant
• Please make sure all these things are done and tick the boxes

- [ ] Changes are OpenShift compatible
- [ ] All added packages (via microdnf or otherwise) have a comment on why they are added
- [ ] Things not downloaded from Red Hat repositories should be mirrored in the Stackable repository and downloaded from there
- [ ] All packages should have (if available) signatures/hashes verified
- [ ] Add an entry to the CHANGELOG.md file
- [ ] Integration tests ran successfully

TIP: Running integration tests with a new product image

The image can be built and uploaded to the kind cluster with the following commands:

bake --product <product> --image-version <stackable-image-version>
kind load docker-image <image-tagged-with-the-major-version> --name=<name-of-your-test-cluster>

See the output of bake to retrieve the image tag for <image-tagged-with-the-major-version>.