pgsql: Fix broken XML formatting in EXPLAIN output for incremental sort

Fix broken XML formatting in EXPLAIN output for incremental sorts.

The ExplainCloseGroup arguments for incremental sort usage data
didn't match the corresponding ExplainOpenGroup.  This only matters
for XML-format output, which is probably why we'd not noticed.

Daniel Gustafsson, per bug #16683 from Frits Jalvingh

Discussion: https://postgr.es/m/16683-8005033324ad34e9@postgresql.org

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/e4538708d58400c8c0336ebabca0b7bdb72e0ff6

Modified Files
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src/backend/commands/explain.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)