pgsql: Doc: fix our example systemd script.

Doc: fix our example systemd script.

The example used "TimeoutSec=0", but systemd's documented way to get
the desired effect is "TimeoutSec=infinity".

Discussion: https://postgr.es/m/164770078557.670.5467111518383664377@wrigleys.postgresql.org

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a1efc8f8c820a1e94eb26f7c93e4c6f6e9b277d6

Modified Files
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doc/src/sgml/runtime.sgml | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)