S3 download failed when cache enabled

When run with download_cache enabled , download-aws_s3_cp task failed with a message:
```
/bin/bash: line 0: cd: /miniwdl_run/_CACHE/download/ops/20230310_184357_aws_s3_cp/work: No such file or directory
```

configuration snippet:
```
[download_cache]
dir = miniwdl_run/_CACHE/download
get = true
put = true
flock = false
```