UPD: run on new builder, use bullseye and install prerequirements

.gitlab-ci.yml

-image: debian-buster:latest
-
+default: 
+    image: debian-bullseye:latest 
+    tags: 
+      - netvs
 # Change pip's cache directory to be inside the project directory since we can
 # only cache local items.
 variables:
@@ -17,6 +19,7 @@ cache:
 before_script:
   - python -V  # Print out python version for debugging
   - pip install build
+  - python3 -m venv || apt-get install python3-venv
 
 stages:
   - build