pgsql: test_ddl_deparse: Don't use pg_class as source for a matview

test_ddl_deparse: Don't use pg_class as source for a matview

Doing so causes a pg_upgrade of a database containing these objects to
fail whenever pg_class changes.  And it's pointless anyway: we have more
interesting tables anyhow.

Discussion: https://postgr.es/m/CAD5tBc+s8pW9WvH2+_z=B4x95FD4QuzZKcaMpff_9H4rS0VU1A@mail.gmail.com

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a2102e1a92bf0b485487b0582f2efaa9ff025556

Modified Files
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src/test/modules/test_ddl_deparse/expected/matviews.out | 2 +-
src/test/modules/test_ddl_deparse/sql/matviews.sql      | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)