[CI] ShortIntegrationTests.yml - don't save cache with date

[dtzSiFive]

While the ccache is small for this (< 100MB), it runs on every commit and saves the updated ccache with the date. These add up, and contribute to our cache quota without adding much -- we only ever use the latest.

This seems to be baked-in to the ccache action we're using, so may need to handle ccache cache management ourselves (as we already do in nightly) to get the desired behavior.

Offhand, I don't see a reason not to just save under 'ccache' or something.

cc #3761 .