Bump alpine from 3.17 to 3.18 in /conformance (#7551)

Bumps alpine from 3.17 to 3.18.

---
updated-dependencies:
- dependency-name: alpine
  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>

conformance/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.17
+FROM alpine:3.18
 ENV SONOBUOY_VERSION 0.56.16
 RUN apk add curl tar gzip
 RUN curl -sfL https://github.com/vmware-tanzu/sonobuoy/releases/download/v${SONOBUOY_VERSION}/sonobuoy_${SONOBUOY_VERSION}_linux_amd64.tar.gz | tar xvzf - -C /usr/bin