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
------
REL_10_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/91709e10aa515614fbe774069635f837c6b5bef9

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(-)