Update tox.ini to bump apache-airflow

Author: knikure

tox.ini

@@ -81,7 +81,7 @@ passenv =
 # Can be used to specify which tests to run, e.g.: tox -- -s
 commands =
     python -c "import os; os.system('install-custom-pkgs --install-boto-wheels')"
-    pip install 'apache-airflow==2.9.0' --constraint "https://raw.githubusercontent.com/apache/airflow/constraints-2.9.0/constraints-3.8.txt"
+    pip install 'apache-airflow==2.9.1' --constraint "https://raw.githubusercontent.com/apache/airflow/constraints-2.9.1/constraints-3.8.txt"
     pip install 'torch==2.0.1+cpu' -f 'https://download.pytorch.org/whl/torch_stable.html'
     pip install 'torchvision==0.15.2+cpu' -f 'https://download.pytorch.org/whl/torch_stable.html'
     pip install 'dill>=0.3.8'