Bump rust from 1.70 to 1.71 in /images/prow-tests (#129)

Bumps rust from 1.70 to 1.71.

---
updated-dependencies:
- dependency-name: rust
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

images/prow-tests/Dockerfile

@@ -229,7 +229,7 @@ RUN git clone https://github.com/kubernetes/kops /tmp/kops && cd /tmp/kops/tests
     go install .
 
 ############################################################
-FROM rust:1.70 AS external-rust-gets
+FROM rust:1.71 AS external-rust-gets
 
 ARG CODESIGN_VERSION=0.22.0
 # change this when a new version with https://github.com/indygreg/apple-platform-rs/pull/20 is cut