ci: resolve failing flask framework tests [backport 2.7] (#8667)

Author: github-actions[bot]

.github/workflows/test_frameworks.yml

@@ -332,6 +332,7 @@ jobs:
         # test_exception_propagation is broken upstream
         run: |
           source .tox/py38/bin/activate
+          pip install "pytest<8.1"
           pip install ../ddtrace
           pip install -e .
           pip install --upgrade MarkupSafe==2.0.1