fix: replace flaky kube-linter action with cached manual install

[pdodgen-revparts]

Summary

• The stackrox/kube-linter-action@v1 download script intermittently fails due to transient GitHub API errors — it uses curl --silent --fail with set -e and no retry logic, causing silent failures across all repos using this workflow
• Replaces with gh release download (authenticated, better error handling) and actions/cache to skip the download entirely on cache hits
• Pins kube-linter to v0.8.1 via KUBE_LINTER_VERSION env var for easy bumping
  https://revolutionparts.atlassian.net/browse/DEVEX-1032

Test plan

• Merge and verify kube-lint passes on an existing PR in encodium/manage
• Confirm cache hit on a subsequent run in the same repo

[cursor]

PR Summary

Low Risk
Low risk CI-only change, but it can affect pipeline reliability if the download or cache key/path is incorrect or if the pinned kube-linter version behaves differently.

Overview
Replaces stackrox/kube-linter-action@v1 with a pinned, manual kube-linter install (KUBE_LINTER_VERSION=0.8.1) using gh release download, then runs ./kube-linter lint against the provided directory.

Adds actions/cache for the kube-linter binary keyed by version to avoid repeated downloads and reduce flakiness from transient GitHub API failures.

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[cursor]

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