Automerge: [CI] Save sccache logs (#155444)

This patch saves the sccache logs to the artifacts. If sccache dies and
the server prints logs, we currently do not collect them anywhere and
they do not get dumped to STDOUT/STDERR. If the process is directly
getting killed (SIGTERM), it seems like it doesn't dump anything, but in
most other cases we should be able to see something.

Related to #155442.

Author: boomanaiden154