pgsql: Fix table name clash in recently introduced test

Fix table name clash in recently introduced test

A few buildfarm animals recently started complaining about the "child"
relation already existing. e056c557aef added a new child table to inherit.sql,
but triggers.sql, running in the same parallel group, also uses a child table.

Rename the new table to inh_child. It maybe worth renaming child, parent in
other tests as well, but that's work for another day.

Discussion: https://postgr.es/m/20230407204530.52q3v5cu5x6dj676@awork3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/728015a47016dcd734c516e43f326ae491b6a3d2

Modified Files
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src/test/regress/expected/inherit.out | 16 ++++++++--------
src/test/regress/sql/inherit.sql | 6 +++---
2 files changed, 11 insertions(+), 11 deletions(-)