robust backward compatibility

tests/backward_compatibility_tests.sh

@@ -38,6 +38,9 @@ pip uninstall -y skypilot
 pip install uv
 uv pip install --prerelease=allow "azure-cli>=2.65.0"
 uv pip install -e ".[all]"
+# In case there are some clusters left from previous tests
+sky down ${CLUSTER_NAME}* -y
+sky jobs cancel -n ${MANAGED_JOB_JOB_NAME}* -y
 cd -
 
 conda env list | grep sky-back-compat-current || conda create -n sky-back-compat-current -y python=3.9