PostgreSQL 14.3 plpython not compatible with Python 3.11

The regression tests for plpython fail with PostgreSQL 14.3 when trying to
build it with the 3.11 (available for testing in a copr build, see below).

Steps to Reproduce:
1. set up a local mock config with Python 3.11 as described in the copr:
https://copr.fedorainfracloud.org/coprs/g/python/python3.11/
2. build postgresql 14.3

Actual results:

More cases of the following failures:

=== make failure: src/pl/plpython/regression.diffs ===
diff -U3
/builddir/build/BUILD/postgresql-14.3/src/pl/plpython/expected/python3/plpython_transaction.out
/builddir/build/BUILD/postgresql-14.3/src/pl/plpython/results/python3/plpython_transaction.out
---
/builddir/build/BUILD/postgresql-14.3/src/pl/plpython/expected/python3/plpython_transaction.out
2022-05-31 20:02:30.754782055 +0200
+++
/builddir/build/BUILD/postgresql-14.3/src/pl/plpython/results/python3/plpython_transaction.out
2022-05-31 20:02:32.867788655 +0200
@@ -70,10 +70,8 @@
return 1
$$;
SELECT transaction_test3();
-ERROR:  spiexceptions.InvalidTransactionTermination: invalid transaction
termination
+ERROR:  SystemError: unknown opcode
CONTEXT:  Traceback (most recent call last):
-  PL/Python function "transaction_test3", line 2, in <module>
-    plpy.execute("CALL transaction_test1()")
PL/Python function "transaction_test3"
SELECT * FROM test1;
a | b
@@ -88,10 +86,8 @@

Also reported as:
https://bugzilla.redhat.com/show_bug.cgi?id=2092085

Regards,
Honza

Honza Horak <hhorak@redhat.com> writes:

Now I read more carefully that this issue was already mentioned by Tom in
the original bug:
https://bugzilla.redhat.com/show_bug.cgi?id=2023272#c7

I was just confused not seeing the fix in the latest version... will try

it.

Here's a quick rebase of that commit onto the v14 branch, in case it
helps.

regards, tom lane