Fix pre-commit isort failure on tests/backends/*.py

[arnaudgelas]

What does this PR do?

Relates to #4805

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Make sure you had fun coding 🙃

[Borda]

@arnaudgelas remove the folder from skip list...

[Borda]

@arnaudgelas mind resolve conflicts 🐰

[arnaudgelas]

@Borda rebased

[codecov]

Codecov Report

Merging #5430 (9a781a2) into release/1.2-dev (ddd9cc1) will not change coverage.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           release/1.2-dev   #5430   +/-   ##
===============================================
  Coverage               93%     93%           
===============================================
  Files                  152     152           
  Lines                10736   10736           
===============================================
  Hits                  9948    9948           
  Misses                 788     788