build: bump actions/cache to v6

[lachieh]

build: bump actions/cache to v6

GitHub deprecated the Node 20 runtime on runners. They now force anything still pinned to Node 20 to run on Node 24 anyway, so this isn't a functional break — the cache already runs on 24. The only thing we get is a deprecation warning on every run:

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@v4.

setup-nub wraps actions/cache in its "Cache nub store" step, so every consumer inherits that warning (e.g. "Detect server changes / Node.js 20 is deprecated" in the murals.plus pipelines). This just bumps the embedded step from actions/cache@v4 to actions/cache@v6 to silence it. Key, paths, and restore-keys are unchanged.

[pullfrog]

no API key found — Pullfrog needs at least one LLM provider API key (e.g. ANTHROPIC_API_KEY, OPENAI_API_KEY, GEMINI_API_KEY) configured as a GitHub Actions secret.

To fix: add the key as a GitHub Actions secret (referenced from your workflow's env: block) or as a Pullfrog secret in the console — or switch this repo to a different model (free models need no key).

Open repo secrets → · Configure model → · Setup docs → · Ask in Discord →

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[GuptaSiddhant]

@colinhacks could this be merged to enable better dev-exp.

[pullfrog]

✅ No new issues found.

Reviewed changes: this PR moves the embedded "Cache nub store" step to actions/cache@v6. I checked the bump against the upstream contract at the v6 tag.

• Bumped actions/cache from v4 to v6 in action.yml. Upstream v6/action.yml runs on node24 and keeps the path / key / restore-keys inputs that setup-nub passes. v6/src/restoreImpl.ts still sets cache-hit to 'true' on an exact hit and 'false' on a restore-keys hit, and leaves it unset on a full miss. The documented cache-hit output that setup-nub re-exports therefore stays accurate. The v6.0.0 and v6.1.0 release notes list only internal changes: an ESM migration and handling for read-only cache access.

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