fix: pin prefect version

setup.cfg

@@ -100,6 +100,12 @@ UI =
     pysimplegui
 workflow =
     prefect>=2.20.25,<3.0
+    # prefect 2.20.25 is the final 2.x release (no backports). Its
+    # GatherTaskGroup subclasses anyio's TaskGroup but doesn't implement
+    # create_task, which newer anyio 4.x made abstract (broken on 4.14,
+    # verified good on 4.6.2); hold anyio to the last verified-good 4.6 line
+    # so the prefect-2.x flow engine can still instantiate task groups.
+    anyio>=4.4.0,<4.7
 tutorial =
     %(dataimport)s
 all =
@@ -118,7 +124,9 @@ dev =
 # Add here test requirements (semicolon/line-separated)
 testing =
     pytest-asyncio
-    prefect
+    # inherit the capped prefect pin (<3.0); a bare "prefect" here resolved to
+    # 3.x in CI, whose server API breaks the prefect-2.20-targeted tests
+    %(workflow)s
     setuptools
     pytest
     pytest-cov

tests/utils/workflow_test.py

@@ -34,7 +34,6 @@
     ],
     log_prints=True,
 )
-@flow
 def osw_python_teams_notify_test_flow():
     """Notify Microsoft Teams channel using a webhook"""
     return 42