ci: Fix remove option -U from pip install

.gitlab-ci.yml

@@ -115,8 +115,8 @@ build-developers-doc:
     - cd ../../src
     - python3 -m venv doc-venv
     - . doc-venv/bin/activate
-    - pip3 install -U -r ../requirements.txt
-    - pip3 install -U pdoc3
+    - pip3 install -r ../requirements.txt
+    - pip3 install pdoc3
     - pdoc --html .
     # Create archive
     - tar cf html.tar ./html