Update tox conf.

tox.ini

@@ -1,8 +1,9 @@
 # See http://tox.readthedocs.org/en/latest/examples.html for samples.
 [tox]
 envlist =
-    py{37,38}-django{18,19,110,111,20,21,22}
-    py{36,37,38,39,310,311}-django{30,31,32,40,41,42}
+    py{36,37}-django{18,19,110,111,20,21,22}
+    py{38,39}-django{30,31,32,40,41,42}
+    py{310,311}-django{30,31,32,40,41,42,50}
 
 skip_missing_interpreters = True
 
@@ -27,3 +28,4 @@ deps =
     django40: Django>=4.0,<4.1
     django41: Django>=4.1,<4.2
     django42: Django>=4.2,<4.3
+    django50: Django>=5.0,<5.1