test/upload-results: use removeprefix() instead of lstrip()

lstrip() is for stripping a class of characters, not removing a string
of text.

test/scripts/upload-results

@@ -37,7 +37,7 @@ def main():
         with open(info_path, "r", encoding="utf-8") as info_fp:
             build_info = json.load(info_fp)
         # strip the PR prefix
-        build_info["pr"] = pr_number.lstrip("PR-")
+        build_info["pr"] = pr_number.removeprefix("PR-")
         with open(info_path, "w", encoding="utf-8") as info_fp:
             json.dump(build_info, info_fp, indent=2)