[ci] Fail CI on broken FPGA runs
[ci] Fail CI on broken FPGA runs

When we introduced the CI runs on FPGAs we downgraded failures to
warnings to ensure that infrastructure problems wouldn't disrupt the
development workflow. The infrastructure has shown to be stable now and
is actually catching real bugs, so we can make the warning an error
again to raise visibility.

Signed-off-by: Philipp Wagner <5a4b10454c30419e54a1570be358a516ff84bb63@lowrisc.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan