Upgrade @actions/cache to 4.0.3

[JoeDupuis]

Upgrade @actions/cache to fix Failed to save: Failed to CreateCacheEntry: Received non-retryable error errors.

Here's a test run with a rails app before the fix: https://github.com/JoeDupuis/test-setup-ruby-fix/actions/runs/15094257150

and after the fix: https://github.com/JoeDupuis/test-setup-ruby-fix/actions/runs/15094275803

The error only show when trying to bust the cache.

More context on this actions/cache issue

[eregon]

From actions/cache#1541 (comment) it seems to mention 4.2.2, ah but that's actions/cache, not the toolkit version with the fix, which seems to be 4.0.2 from https://github.com/actions/cache/releases/tag/v4.2.2.
And https://github.com/actions/toolkit/blob/main/packages/cache/package.json#L3 is 4.0.3.
OK, thank you.

BTW it's a warning not an error but yes good to avoid unfixable warnings.