downloadToFile caches HTTP error responses. AccessDenied XML saved as install.sh on persistent runners

On persistent self-hosted runners, the `/tmp/` directory is persistent between runs. Coupled with an error that was returned on the first execution, `cimon-action` subsequently fails all further runs for two reasons:

First, `downloadToFile` does not check the HTTP response status code before writing to disk. If the S3 URL returns a non-200 response (e.g. 403 AccessDenied), the error body is written verbatim to `/tmp/install.sh`.

Second, The cache guard checks only for file existence, not file integrity. On subsequent runs, `existsSync('/tmp/install.sh')` returns true for the corrupt file and the re-download is permanently skipped.