Append results to zip file

This may greatly increase the archive file size which we need to simplify our matrix.
But at least we should get some more insights into failing tests.

Author: emanlove

atest/run.py

@@ -259,7 +259,7 @@ def create_zip():
     zip_name = f"rf-{robot_version}-python-{python_version}.zip"
     zip_path = os.path.join(ZIP_DIR, zip_name)
     print("Zip created in: %s" % zip_path)
-    zip_file = zipfile.ZipFile(zip_path, "w")
+    zip_file = zipfile.ZipFile(zip_path, "a")
     for root, dirs, files in os.walk(RESULTS_DIR):
         for file in files:
             file_path = os.path.join(root, file)