ci: install zip on Linux and make artifact checks non-fatal when absent

Author: jetsung

.github/workflows/quality.yml

@@ -59,6 +59,8 @@ jobs:
       run: |
         npm run build
 
+        ls -1
+
         # Check that build produces expected files
         test -f json-format-converter-chrome.zip || (echo "Chrome ZIP not created" && exit 1)
         test -f json-format-converter-firefox.zip || (echo "Firefox ZIP not created" && exit 1)