Use /tmp as unix socket directory in the CI

[jeltz]

Since the Ubuntu packages uses /run/postgresql as the unix socket directory by default and that directory is owned by the postgres user we used to change owner of /run/postgresql but instead we can just use /tmp and simplify our setup.

This way we do not even have to kill the default instance of PostgreSQL.

PG-0

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.46%. Comparing base (81ca012) to head (c023146).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #823   +/-   ##
=======================================
  Coverage   88.46%   88.46%           
=======================================
  Files           3        3           
  Lines        1318     1318           
  Branches      187      187           
=======================================
  Hits         1166     1166           
  Misses         77       77           
  Partials       75       75           

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