pgsql: Improve numeric_power() tests for large integer powers.

Improve numeric_power() tests for large integer powers.

Two of the tests added by 4dd5ce2fd fail on buildfarm member
castoroides, though it's not clear why. Improve the tests to report
the actual values produced, if they're not what was expected.

Apply to v11 only for now, until it's clearer what's going on.

Branch
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REL_11_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/434ddfb79afea5c515f17fc5febac15afc26d017

Modified Files
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src/test/regress/expected/numeric.out | 8 ++++----
src/test/regress/sql/numeric.sql      | 4 ++--
2 files changed, 6 insertions(+), 6 deletions(-)