urwid: unlock v3 (#7030)

* Urwid v3 has landed.
* Luckily, we don't appear to be on the bad side of any of the breaking
  changes.
* So keep v2 support for now, but add v3 support going forward.

Author: oliver-sanders

conda-environment.yml

@@ -16,7 +16,7 @@ dependencies:
   - psutil >=5.6.0
   - python
   - pyzmq >=22
-  - urwid >=2.2,<3,!=2.6.2,!=2.6.3
+  - urwid >=2.2,<4,!=2.6.2,!=2.6.3
 
 # optional dependencies
   #- pandas >=1.0,<2

setup.cfg

@@ -71,7 +71,7 @@ install_requires =
     psutil>=5.6.0
     pyzmq>=22
     # NOTE: exclude two urwid versions that were not compatible with Tui
-    urwid>=2.2,!=2.6.2,!=2.6.3,<3
+    urwid>=2.2,!=2.6.2,!=2.6.3,<4
 
 [options.packages.find]
 include = cylc*