Bump golang from 1.22.7 to 1.22.8 in /images/prow-tests

Bumps golang from 1.22.7 to 1.22.8.

---
updated-dependencies:
- dependency-name: golang
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

images/prow-tests/Dockerfile

@@ -196,7 +196,7 @@ RUN curl -fsSL "https://github.com/protocolbuffers/protobuf/releases/download/v$
     && rm protoc.zip
 # protoc-gen-gogofaster is installed below
 
-FROM golang:1.22.7 AS external-go-latest
+FROM golang:1.22.8 AS external-go-latest
 # Capture the version that dependabot bumps so that we can install it into the base image
 RUN go version | cut -d' ' -f3 > /golang.version