pin pytest for gwcs tests to deal with doctestplus issue

.github/workflows/ci.yml

@@ -96,6 +96,8 @@ jobs:
           python-version: 3.9
       - name: Install asdf-wcs-schemas
         run: cd asdf-wcs-schemas && pip install .
+      - name: Install older pytest
+        run: pip install "pytest<8.1"
       - name: Install gwcs
         run: cd gwcs && pip install -e .[test]
       - name: Pip Freeze

pyproject.toml

@@ -42,7 +42,7 @@ docs = [
     'sphinx-rtd-theme',
 ]
 test = [
-    'pytest >= 4.6.0',
+    'pytest >= 4.6.0, <= 8.1',
     'asdf >= 2.8.0',
     'asdf-astropy',
 ]