Fix double connection issue

[andrea-pasquale]

Closes #114.
As noted by @aorgazf, when running qq the platform was connecting twice to the instruments.
The double connection was caused by:

• set_backend which for qibolab performs also the connection with the instruments
• allocating a platform with the updated_runcard, i.e. the platform runcard which is continuosly updated when we run multiple routines.

In this PR I solved this issue by calling set_backend once with the updated_runcard directly.
Let me know what you think.

[codecov]

Codecov Report

Merging #115 (1df4f73) into main (68c4261) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #115   +/-   ##
=======================================
  Coverage   21.58%   21.58%           
=======================================
  Files          12       12           
  Lines         658      658           
=======================================
  Hits          142      142           
  Misses        516      516           

Flag	Coverage Δ
unittests	21.58% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

[stavros11]

Thanks, it works for me. I checked and the new_platform.yml runcard is updated and reloaded every time for the next routine, when launching more than one routines.

[andrea-pasquale]

Thanks. I'll merge this now.