chore(github): update actions from deprecated node-20 versions

[keturn]

Summary

GitHub Actions have been reporting "Node.js 20 actions are deprecated." and warning that runners will use Node 24 next month week (June 2nd, 2026).

This updates the actions that I found triggering that warning to their current versions. I did take a look at the release notes for the actions, and didn't see breaking changes that are obviously applicable to our configuration.

• https://github.com/ppremk/lfs-warning has no newer version. Cross your fingers and hope it continues to work, or PR an update for it.
• https://github.com/astral-sh/setup-uv/releases has by far the most releases since the previous target (v5). Our configuration is nothing fancy so it should continue to work despite the changes, unless newer versions of the action turn out to be grumpy about working with such an outdated version of uv.
• some updates advertised better caching by default, but I didn't investigate to see if e.g. the cache step in install-frontend-action has been made redundant.

QA Instructions

I'm not sure if this can entirely be tested on a PR from a fork. GitHub may limit which actions can be modified by an external PR, and some of the actions depend on triggers that don't come from a branch.

[keturn]

docs is a pnpm project that runs a python script? wild.

[joshistoast]

docs is a pnpm project that runs a python script? wild.

Yea there's no other good way to get dynamic API typings from python to be shown in the markdown.

[joshistoast]

all tests pass and code changes look good