Travis-CI: upgrade to bionic broke merge builds

[SethTisue]

PR validation builds aren't affected, which is why this wasn't caught before scala/scala#7432 was merged

btw I did check that bionic is an upgrade, not a downgrade. bionic is ubuntu 18, xenial was ubuntu 16. so I think this isn't wasted work as we'd likely need to upgrade eventually

GitHub Actions has already been on 18 for a while and is presently moving to 20, as per actions/runner-images#1816

[SethTisue]

@lrytz is looking into it:

the jobs end with $ (cd admin && ./init.sh), which does
sensitive() {
... perl ...
... openssl ...
}
sensitive >/dev/null 2>&1
so probably one of these commands is failing
i pushed this to a branch > scala/scala@708367b
https://travis-ci.org/github/scala/scala/jobs/749052208 (edited)
the output is truncated, but there's some message at the end WARNING : deprecated key derivation that comes from openssl
openssl went from 1.0 to 1.1 https://packages.ubuntu.com/xenial/openssl > https://packages.ubuntu.com/bionic/openssl
https://askubuntu.com/questions/1093591/how-should-i-change-encryption-according-to-warning-deprecated-key-derivat
maybe this https://stackoverflow.com/questions/39637388/encryption-decryption-doesnt-work-well-between-two-different-openssl-versions
testing with -md md5 https://travis-ci.org/github/scala/scala/builds/749073379