The test jobs used actions/cache/restore with fail-on-cache-miss,
which aborted when the cache key was scoped to another PR or had
been evicted, even though the build job reported success.
Drop fail-on-cache-miss and add a fallback rebuild in the test
job, gated on the cache-hit output. Fast path is unchanged; on
miss the test job rebuilds locally and proceeds.
Andrew Hutchings
Tobias Frauenschläger
Josh Holtrop
gojimmypi
Juliusz Sosinowicz