Investigate sscache stop CI failures

[bnoordhuis]

trafficstars

Fails intermittently like this when executing sccache --show-stats:

/home/runner/work/_temp/c2b88417-fdca-4378-b8c3-66cea7ddc094.sh:
line 1: sccache: command not found

I've removed the CI phase that stops sccache in #876 because it was getting in the way of getting work done but @piscisaureus would like to see it re-enabled because it prints cache statistics, i.e., shows if it's active and effective.