Add a Python 3.14 test environment to the default list in tox

I had to set the minimum pytest version for Python 3.14 to pytest 7.3.2,
because older versions of pytest use ast.Str, which was removed in 3.14.

Author: diazona

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py{37,38,39,310,311,312,313,py3}{,-smtp},lint
+envlist = py{37,38,39,310,311,312,313,314,py3}{,-smtp},lint
 recreate = True
 isolated_build = True
 
@@ -22,8 +22,9 @@ deps =
     # works with your code. Don't forget to modify the corresponding entries in
     # the Github workflows configuration file if you do change these lower
     # bounds.
-    pytest >=4.6, <9; python_version<'3.10'
-    pytest >=6.2.4, <9; python_version>='3.10'
+    pytest >=4.6, <9; python_version <'3.10'
+    pytest >=6.2.4, <9; python_version >='3.10' and python_version <'3.14'
+    pytest >=7.3.2, <9; python_version >='3.14'
     pytest-cov !=6.2.0
     requests
 extras =