The test would fail in an environment including a certificate file in
~/.postgresql/.  bdd6e9ba fixed a similar failure, and d6e612f8 introduced
the same problem again with a new test.

Author: Kyotaro Horiguchi
Discussion: https://postgr.es/m/20200804.120033.31225582282178001.horikyota.ntt@gmail.com
Backpatch-through: 13