sccache in github actions

[swatanabe]

The output from sccache -s is useless, because all the statistics are lost when the sccache daemon exits.

I was able to get the actual stats by printing them right after running make.

Compile requests                   2651
Compile requests executed          2142
Cache hits                          343
Cache hits (Rust)                   343
Cache misses                       1760
Cache misses (C/C++)                482
Cache misses (Rust)                1278
Cache timeouts                        0
Cache read errors                     0
Forced recaches                       0
Cache write errors                    0
Compilation failures                 39
Cache errors                          0
Non-cacheable compilations            0
Non-cacheable calls                 483
Non-compilation calls                26
Unsupported compiler calls            0
Average cache write               0.001 s
Average compiler                  3.132 s
Average cache read hit            0.006 s
Failed distributed compilations       0

Non-cacheable reasons:
crate-type                          391
-                                    66
unknown source language              26

Cache location                  Local disk: "/home/runner/work/psibase/psibase/.caches/sccache"
Use direct/preprocessor mode?   yes
Version (client)                0.8.1
Cache size                          200 MiB
Max cache size                      200 MiB

It looks like the cache is too small to be effective. Note that there were no changes to any rust code from the previous successful build.