Test suite hangs since PostgreSQL 14.5 release.

Examples of tests hanging:

• tests/test_client_cursor.py::test_executemany
• tests/test_pipeline.py::test_pipeline_processed_at_exit

From the release notes, the breakage must come from:

Improve libpq's handling of idle states in pipeline mode (Álvaro Herrera, Kyotaro Horiguchi)

This fixes “message type 0x33 arrived from server while idle” warnings, as well as possible loss of end-of-query NULL results from PQgetResult().

which was done after the report in #314.