update python path to 3.9 for site-packages

Been having issues getting this to build on Ubuntu 20 and this change
got it working. I don't remember the details on why we need this but we
are now installing python3.9 in our CI images so make it match.

Change-Id: Ic72d32a612d186359b78d098697477db9132c8ad
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index 7706ef6..4d5fb1b 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -733,7 +733,7 @@
 
 ENV DEBIAN_FRONTEND noninteractive
 
-ENV PYTHONPATH "/usr/local/lib/python3.8/site-packages/"
+ENV PYTHONPATH "/usr/local/lib/python3.9/site-packages/"
 
 # Sometimes the ubuntu key expires and we need a way to force an execution
 # of the apt-get commands for the dbgsym-keyring.  When this happens we see