[ci] Break off linting into its own job
[ci] Break off linting into its own job

This should stop format/clippy errors from blocking the build
altogether.

Signed-off-by: Miguel Young de la Sota <71b8e7f4945fd97b98544cf897992af89646547a@google.com>

lowRISC/manticore,lowRISC/manticore,lowRISC/manticore