Add sphinx81 testenv

Author: abitrolly

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 envlist =
     py{38,39,310}-sphinx{60,61,62,70,71}{-qa}
-    py{39,310,311,312}-sphinx{72,73,74,80}{-qa}
+    py{39,310,311,312}-sphinx{72,73,74,80,81}{-qa}
     py{310,311,312}-sphinx{latest,dev}{-qa}
 
 [testenv]
@@ -17,6 +17,7 @@ deps =
     sphinx71: Sphinx>=7.1,<7.2
     sphinx72: Sphinx>=7.2,<7.3
     sphinx80: Sphinx>=8.0,<8.1
+    sphinx81: Sphinx>=8.1,<8.2
     sphinxlatest: Sphinx
     sphinxdev: https://github.com/sphinx-doc/sphinx/archive/refs/heads/master.zip
 allowlist_externals =