BF: correct import backend_pysound after module name change

[mh105]

The pysoundcard file name has been changed to backend_pysound instead of backend_pysoundcard. This BF fixes an attempt to import it.

This is cherry-picked from #6436, now PR into release.

[codecov]

Codecov Report

Attention: Patch coverage is 42.85714% with 4 lines in your changes missing coverage. Please review.

Project coverage is 51.47%. Comparing base (d5016a0) to head (06745f9).
Report is 35 commits behind head on release.

Additional details and impacted files

@@             Coverage Diff             @@
##           release    #6524      +/-   ##
===========================================
- Coverage    52.16%   51.47%   -0.70%     
===========================================
  Files          335      333       -2     
  Lines        61961    61785     -176     
===========================================
- Hits         32322    31802     -520     
- Misses       29639    29983     +344     

Components	Coverage Δ
app	∅ <ø> (∅)
boilerplate	∅ <ø> (∅)
library	∅ <ø> (∅)
vm-safe library	∅ <ø> (∅)