tests: migrate from nosetests to pytest

[dimitri]

Summary

Switch the Python test runner from nosetests to pytest. nosetests crashes on Python 3.11+ because collections.Callable was removed in Python 3.10 and nose's suite.py still references it. pytest is the modern replacement and is available in Bullseye apt as python3-pytest.

Changes

Dockerfile

• Replace pipenv (unused) with python3-pytest in the apt install block
• Quote 'pyroute2>=0.5.17' so the shell does not strip the >= operator

Makefile / Makefile.citus

• NOSETESTS → PYTEST = python3 -m pytest (reliable regardless of binary name; Debian's python3-pytest installs py.test-3, not pytest)
• TEST_ARGUMENT format: nosetests --where=tests --tests=foo,bar → pytest path style tests/foo.py tests/bar.py
• Use tests/*.py glob (not tests/) to avoid descending into tests/tablespaces/ which has its own make target and import layout
• pytest flags: -v -s -x replace --verbose --nologcapture --nocapture --stop

tests/network.py

• Replace universal_newlines=True with encoding='utf-8', errors='replace' in both NSPopen calls so non-ASCII bytes from pg_autoctl output are replaced rather than raising UnicodeDecodeError
• Add LC_ALL=C LANG=C to subprocess env so PostgreSQL produces ASCII-only error messages inside network namespaces (pyroute2 ≥ 0.5.17 is strict about UTF-8 decoding)

tests/tablespaces/conftest.py (new)

• Add project root to sys.path so tablespace tests can import as from tests.tablespaces.xxx import …; nosetests satisfied this implicitly, pytest does not

tests/pgautofailover_utils.py

• Fix run_sql_query when autocommit=True: psycopg2's with conn: context manager wraps an implicit BEGIN even when autocommit is on, blocking DDL like CREATE TABLESPACE; use explicit commit/rollback/finally instead

.github/workflows/run-tests.yml

• Add needs: style_checker to build_images so a style failure stops CI before any image builds start

Testing

Validated locally: TEST=single make run-test with PG17 — 88 passed, 0 failed (8 min).