Fixing compiler rules when dealing with qubit strings

[andrea-pasquale]

The virtual phases were not properly updated when executing circuits containing strings.
Thanks @stavros11 for spotting the issue.

Checklist:

• Reviewers confirm new code works as expected.
• Tests are passing.
• Coverage does not decrease.
• Documentation is updated.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.32%. Comparing base (11a34bd) to head (1d8e3e2).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #937   +/-   ##
=======================================
  Coverage   70.32%   70.32%           
=======================================
  Files          64       64           
  Lines        6679     6679           
=======================================
  Hits         4697     4697           
  Misses       1982     1982           

Flag	Coverage Δ
unittests	70.32% <100.00%> (ø)

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