fix: ModuleNotFoundError: No module named 'selenium'

Author: dlachaume

.github/workflows/test-client.yml

@@ -242,5 +242,6 @@ jobs:
         working-directory: mithril-client-wasm
         shell: bash
         run: |
+          pip install selenium
           python3 run-firefox-headless.py
           ./analyze-headless-tests-results.sh firefox-results.html