[Tracking issue] sccache no longer work in nightly CI

[tesuji]

Waiting for mozilla/sccache#488.

[tesuji]

mozilla/sccache#488 fixed. Waiting for new sccache release.

[Dylan-DPC-zz]

@lzutao scache has released a new version, CI looks fine, anything else?

[tesuji]

I am thinking about caching target/ dir instead of using sccache. Will try a look and
investigate it later.

[tesuji]

Now we moved to GitHub actions, but the CI provider hasn't supported caching yet. We could close this issue or wait for CI feature.

[ehuss]

I'm going to close, as I probably won't be adding CI caching back in the foreseeable future.