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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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/70293e946e60bb7eb58f74656667458406a1b461

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(-)