Add the x86_64-unknown-linux-musl rust target in the CI job that needs it
Add the x86_64-unknown-linux-musl rust target in the CI job that needs it

That used to be in travis-musl-openssl.sh, which we removed.

mozilla/sccache,luser/sccache2,mozilla/sccache,glandium/sccache,glandium/sccache,luser/sccache2,luser/sccache2,mozilla/sccache,glandium/sccache,glandium/sccache,luser/sccache2