diff --git a/environment.yml b/environment.yml
index 057b8466fe16..27624759ea86 100644
--- a/environment.yml
+++ b/environment.yml
@@ -63,7 +63,7 @@ dependencies:
   - psutil
   - prek
   - pydocstyle>=5.1.0
-  - pytest!=4.6.0,!=5.4.0,!=8.1.0,<9.1.0
+  - pytest!=4.6.0,!=5.4.0,!=8.1.0
   - pytest-cov
   - pytest-rerunfailures
   - pytest-timeout
diff --git a/lib/matplotlib/tests/test_mlab.py b/lib/matplotlib/tests/test_mlab.py
index 82f877b4cc01..4f2ae49f4772 100644
--- a/lib/matplotlib/tests/test_mlab.py
+++ b/lib/matplotlib/tests/test_mlab.py
@@ -207,7 +207,8 @@ def test_detrend_linear_2d(self):
     scope='class')
 class TestSpectral:
     @pytest.fixture(scope='class', autouse=True)
-    def stim(self, request, fstims, iscomplex, sides, len_x, NFFT_density,
+    @classmethod
+    def stim(cls, request, fstims, iscomplex, sides, len_x, NFFT_density,
              nover_density, pad_to_density, pad_to_spectrum):
         Fs = 100.
 
@@ -323,11 +324,6 @@ def stim(self, request, fstims, iscomplex, sides, len_x, NFFT_density,
         if iscomplex:
             y = y.astype('complex')
 
-        # Interestingly, the instance on which this fixture is called is not
-        # the same as the one on which a test is run. So we need to modify the
-        # class itself when using a class-scoped fixture.
-        cls = request.cls
-
         cls.Fs = Fs
         cls.sides = sides
         cls.fstims = fstims
diff --git a/pyproject.toml b/pyproject.toml
index b63ce715ed9e..cf0cde26cdce 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -129,7 +129,7 @@ test = [
     "certifi",
     "coverage!=6.3",
     "psutil; sys_platform != 'cygwin'",
-    "pytest!=4.6.0,!=5.4.0,!=8.1.0,<9.1.0",
+    "pytest!=4.6.0,!=5.4.0,!=8.1.0",
     "pytest-cov",
     "pytest-rerunfailures!=16.0",
     "pytest-timeout",