[API][Related figure] The response to link streetcodes is 200 OK, but they have already been linked

[iskoryk]

trafficstars

Environment: all Reproducible: always Build found: c648525

Preconditions

1. Open Postman.
2. Choose the POST method.
3. Enter valid endpoints.

Steps to reproduce 1.1. Add valid data for existing and unlinked streetcodes, such as 1045&1043. 1.2. Send request.

2. Send the request a second time.

3.1. Change the ID sequence in the request to 1043&1045. 3.2. Send the request.

Actual result

1. Response - 200 OK.
2. Response - 200 OK.
3. Response - 200 OK.

Expected result

1. Response - 200 OK.
2. Response - 400 Bad request "The streetcodes are already linked".
3. Response - 400 Bad request "The streetcodes are already linked".

User story: #40