Update cache dependencies

[AdamVig]

Update gocache and atomicfile to include the cache-integrity fixes merged upstream.

I found these while investigating a corrupted entry served by our remote Go build cache in CI, which uses go-cache-plugin. The S3 objects I sampled were intact, so I traced possible corruption paths through the plugin's runner-local staging layer.

The gocache update includes creachadair/gocache#6. A short S3 response ending with
a clean EOF previously could be committed to the local cache with its shorter actual size, then later returned as a valid cache hit. gocache now verifies the copied size against the object's declared size before publishing it.

The atomicfile update includes creachadair/atomicfile#1. WriteAll now aborts its transaction on an explicit input read error and reports close or rename failures, instead of potentially publishing a partial file while returning an error to the caller.