Add Flask 2.1

Author: jwhitlock

tests/constraints/flask-2.1.txt

@@ -0,0 +1 @@
+Flask<2.2

tox.ini

@@ -6,7 +6,7 @@ envlist =
     py38-docs
     py{37,38,39,310}-dj32
     py{38,39,310}-dj{40}
-    py{37,38,39,310}-fl{012,10,11,20}
+    py{37,38,39,310}-fl{012,10,11,20,21}
     py{37,38,39}-s{20}
 
 [gh-actions]
@@ -25,19 +25,20 @@ setenv =
 deps =
     -rtests/requirements/default.txt
     dj{32,40}: -rtests/requirements/django.txt
-    fl{012,10,11,20}: -rtests/requirements/flask.txt
+    fl{012,10,11,20,21}: -rtests/requirements/flask.txt
     s{20}: -rtests/requirements/sanic.txt
     dj32: -ctests/constraints/django-3.2.txt
     dj40: -ctests/constraints/django-4.0.txt
     fl012: -ctests/constraints/flask-0.12.txt
     fl10: -ctests/constraints/flask-1.0.txt
     fl11: -ctests/constraints/flask-1.1.txt
     fl20: -ctests/constraints/flask-2.0.txt
+    fl21: -ctests/constraints/flask-2.0.txt
     s20: -ctests/constraints/sanic-20.txt
 commands =
     python --version
     dj{32,40}: pytest tests/core/ tests/django --nomigrations {posargs:}
-    fl{012,10,11,20}: pytest tests/core/ tests/flask/ {posargs:}
+    fl{012,10,11,20,21}: pytest tests/core/ tests/flask/ {posargs:}
     s{19,20}: pytest tests/core/ tests/sanic/ {posargs:}
 
 [testenv:py38-docs]