fix(tests): Etag must be wrapped by "

[Xuanwo]

R2 has strong requirement for Etag:

[2023-05-07T17:34:30Z ERROR opendal::services] service=s3 operation=read path=df189c54-4664-433d-9c85-ed8f830f55cf range=0- -> failed: Unexpected (permanent) at read => S3Error { code: "InvalidArgument", message: "Invalid Argument: If-Match each ETag must be surrounded by double quotes, got 'invalid_etag'.", resource: "", request_id: "" }
    
    Context:
        response: Parts { status: 400, version: HTTP/1.1, headers: {"date": "Sun, 07 May 2023 17:34:30 GMT", "content-type": "application/xml", "content-length": "203", "connection": "keep-alive", "server": "cloudflare", "cf-ray": "7c3b36ce3b1bc729-SEA"} }
        service: s3
        path: df189c54-4664-433d-9c85-ed8f830f55cf
        range: 0-