fix: Add scan regex for failing functional tests

[sitaram-kalluri]

- What I did
Add a work around to fix the failing functional tests in the following link https://github.com/atsign-foundation/at_server/actions/runs/6650002663/job/18069387859

The server response is sent in two packets where as below

Server Response: data:["00478077-0cac-48eb-aa4b-cc43de28a82f.default_enc_private_key.__manage@sitaram"<trimmed>"bce50954-ff3a-47dc-9216-6f368205dd3d.default_self_e

Server Response: nc_key.__manage@sitaram",<trimmed>"lastname.wavi@sitaram"worknumber-267927159.wavi@sitaram"]

In test, socket messageHandler method has following condition to add response to the queue:
if (data.last == 64 && data.contains(10)) which looks for the "@" and "\n". So the response received in the first packet (which starts with "data:" is not added to queue)

In the second packet, though there is a key, since it does not start with "data:", the read assumes that it is not a valid a response and ignores it.

As a work around, add regex to the scan verb to reduce the number of keys in the scan response.