pgsql: Fix broken collate.icu.utf8 test in v12 branch.

Fix broken collate.icu.utf8 test in v12 branch.

collate.icu.utf8.sql is not run by default before v13, and commits
9c4757491/46d9be5ef evidently didn't bother to test it, with
the completely predictable result that it was broken.
We didn't have enable_incremental_sort in v12, plus EXPLAIN makes
different table alias choices than later branches.

Per buildfarm member copperhead.

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/0ef9ac290ff3370f345fa08091c6586fecd8354f

Modified Files
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src/test/regress/expected/collate.icu.utf8.out | 64 +++++++++++++-------------
src/test/regress/sql/collate.icu.utf8.sql | 2 -
2 files changed, 31 insertions(+), 35 deletions(-)