pgsql: Fix documentation comments for test CA config files

Fix documentation comments for test CA config files

The config files which are used to generate the server and client
CAs claimed that these were self-signed, when they in reality are
signed by the root_ca (which however is self-signed).  Reword the
comments to match.

Author: David Zhang <david.zhang@highgo.ca>
Discussion: https://postgr.es/m/12f4c425-45fe-480f-a692-b3ed82ebcb33@highgo.ca

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/6a6b7f5de3ff0dad46aab9e8e17a3747370199a3

Modified Files
--------------
src/test/ssl/conf/client_ca.config | 8 +++++---
src/test/ssl/conf/root_ca.config   | 2 +-
src/test/ssl/conf/server_ca.config | 8 +++++---
3 files changed, 11 insertions(+), 7 deletions(-)