pgsql: Update plpython_subtransaction alternative expected files

Update plpython_subtransaction alternative expected files

The original patch only targeted Python 2.6 and newer, since that is
what we have supported in PostgreSQL 13 and newer. For older
branches, we need to fix it up for older Python versions.

Branch
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REL9_6_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/ec52b886d1dd8c08993b391753d450488e18f330

Modified Files
--------------
src/pl/plpython/expected/plpython_subtransaction.out | 2 +-
src/pl/plpython/expected/plpython_subtransaction_0.out | 9 ++++++---
src/pl/plpython/expected/plpython_subtransaction_5.out | 9 ++++++---
src/pl/plpython/sql/plpython_subtransaction.sql | 2 +-
4 files changed, 14 insertions(+), 8 deletions(-)