fix: pin prefect version

Author: simontaurus

setup.cfg

@@ -118,7 +118,9 @@ 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