Cap version of Flet, to avoid "Event loop is closed" error

ugh i really hate to do that, but nothing else did the trick

setup.cfg

@@ -24,11 +24,18 @@ classifiers =
 
 [options]
 install_requires =
-        flet
         psycopg2
         rattail[db]
         typer
 
+        # TODO: unfortunately the latest Flet versions as of writing
+        # (to 0.22.1) include a bug..when running `wuttapos open`
+        # command then quitting the app, you get an error "Event loop
+        # is closed" - i tried several versions of python (to 3.12.3)
+        # but nothing worked despite the claims made in github issue,
+        # https://github.com/flet-dev/flet/issues/2848
+        flet<0.21
+
 packages = find:
 include_package_data = True
 # zip_safe = False