ci(tox): mypy permanently fixated at 1.3 for stub testsuite

Multiple problems with mypy / pytest-mypy-plugin interaction:
- Starting from mypy 1.4, output is dependant on python version by default, test suite fails for python < 3.10 unless conditional file tests are used
- 'python_version' mypy setting not honored (typeddjango/pytest-mypy-plugins#47)
- Even if above bug is fixed, it's impossible to upgrade because jinja2 doesn't support all chevron template, test suite needs substantial changes
OTOH, annotation itself is compatible with mypy 1.5 (not 1.6 tho)

.github/workflows/pr.yml

@@ -35,7 +35,7 @@ jobs:
         workdir: lxml-stubs
         fail_on_error: true
         ignore_note: true
-        setup_command: pip install mypy>=1.1,<1.4
+        setup_command: pip install mypy==1.5.1
         setup_method: install
         install_types: false
 

tox.ini

@@ -18,7 +18,8 @@ deps =
 
 [testenv:py{38,39,310,311,312}-stub]
 deps =
-    {[testenv:mypy]deps}
+    {[common_dep]deps}
+    mypy == 1.3.0
     pytest-mypy-plugins ~= 1.10, != 1.10.0
 commands = pytest {posargs:test-stub}
 
@@ -44,7 +45,7 @@ commands =
 [testenv:mypy]
 deps =
     {[common_dep]deps}
-    mypy >= 1.2, < 1.4
+    mypy >= 1.2, < 1.6
 package = skip
 commands = mypy {posargs:lxml-stubs}