pgsql: Doc: add information about partition locking

Doc: add information about partition locking

The documentation around locking of partitions for the executor startup
phase of run-time partition pruning wasn't clear about which partitions
were being locked.  Fix that.

Reviewed-by: Tender Wang <tndrwang@gmail.com>
Discussion: https://postgr.es/m/CAApHDvp738G75HfkKcfXaf3a8s%3D6mmtOLh46tMD0D2hAo1UCzA%40mail.gmail.com
Backpatch-through: 13

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/ebbdaf1fd59d3bad4bb0aee346ad6f8a225549d1

Modified Files
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doc/src/sgml/ddl.sgml | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)