Gitea Runner 4.0.0 adds built-in checkout and S3 cache

Gitea Runner 4.0.0 changes cache routing so jobs send cache requests through their runner, requiring users of remote Docker or bridge networking to review cache reachability.

The release also adds the native 'builtin:checkout' action and S3-compatible shared cache storage, removing the need for Node in checkout jobs and a separate cache server for shared caches.

OpenTelemetry tracing, self-hosted action references, and '--umask' support in 'container.options' are also included, while 'valid_volumes' now uses doublestar matching.