pgsql: Make the integerset test more verbose.

Make the integerset test more verbose.

Buildfarm member 'woodlouse' failed one of the tests, and I'm not sure
which test failed. Better to print the names of the tests, so that it
will appear in the regression.diffs on failure.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/608c5f4347acefdbb2663b9fb6deab079b4b3c8b

Modified Files
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.../test_integerset/expected/test_integerset.out   | 27 ++++++++++++++++++----
.../test_integerset/sql/test_integerset.sql        |  8 ++-----
2 files changed, 24 insertions(+), 11 deletions(-)