test(syslog): each integration step its own session (#5999)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/integration/test_syslog.py

@@ -64,6 +64,7 @@ def test_an_unknown_sender_is_offered_and_an_added_one_kept(app):
             lines = (await s.execute(select(SyslogLine))).scalars().all()
             assert [(ln.app, ln.hostname, ln.message, ln.severity) for ln in lines] == [("kernel", "synnas", "kept", 3)]
             assert (await s.get(SyslogSource, src_id)).lines_total == 3
+        async with app.db_sessionmaker() as s:
             async with s.begin():
                 await s.execute(delete(SyslogSource))
 
@@ -102,6 +103,7 @@ def test_the_ring_keeps_each_source_within_its_window_and_cap(app):
             kept = (await s.execute(select(SyslogLine.source_id))).scalars().all()
             assert counts == {"age_pruned": 1, "size_pruned": 2}
             assert kept.count(a_id) == 3 and kept.count(b_id) == 2
+        async with app.db_sessionmaker() as s:
             async with s.begin():
                 await s.execute(delete(SyslogSource))