fix(ci): dynamically check if unit-3.9 session exists before running

Author: chalmerlowe

ci/run_single_test.sh

@@ -79,8 +79,13 @@ case ${TEST_TYPE} in
             retval=$?
             ;;
         "3.9")
-            nox -s unit-3.9
-            retval=$?
+            if nox --list-sessions | grep -q "unit-3.9"; then
+                nox -s unit-3.9
+                retval=$?
+            else
+                echo "Skipping unit-3.9 as it is not supported by this package."
+                retval=0
+            fi
             ;;
         "3.10")
             nox -s unit-3.10