Remove setting logger name to empty string if root

[johannaengland]

Dependent on #2901.

Since Python 3.9 getLogger('root') also returns the root logger: python/cpython#15077

Mentioned also here: https://docs.python.org/3/whatsnew/3.9.html#changes-in-the-python-api

[github-actions]

Test results

       9 files         9 suites   7m 46s ⏱️
3 320 tests 3 320 ✔️ 0 💤 0 ❌
6 379 runs  6 379 ✔️ 0 💤 0 ❌

Results for commit 6badf05.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.35%. Comparing base (b8d6d52) to head (0536ed0).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2912   +/-   ##
=======================================
  Coverage   56.35%   56.35%           
=======================================
  Files         603      603           
  Lines       43862    43858    -4     
  Branches       48       48           
=======================================
- Hits        24719    24718    -1     
+ Misses      19131    19128    -3     
  Partials       12       12           

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