feat(falcon): Run test suite with Falcon 4.0.0b3 (#3644)

Author: sentrivana

tox.ini

@@ -117,6 +117,7 @@ envlist =
     # Falcon
     {py3.6,py3.7}-falcon-v{1,1.4,2}
     {py3.6,py3.11,py3.12}-falcon-v{3}
+    {py3.8,py3.11,py3.12}-falcon-v{4}
     {py3.7,py3.11,py3.12}-falcon-latest
 
     # FastAPI
@@ -429,6 +430,8 @@ deps =
     falcon-v1: falcon~=1.0
     falcon-v2: falcon~=2.0
     falcon-v3: falcon~=3.0
+    # TODO: update to 4.0 stable when out
+    falcon-v4: falcon==4.0.0b3
     falcon-latest: falcon
 
     # FastAPI