[PR #6375/eccd9099 backport][3.9] Add a test for circular imports in the project

[patchback]

This is a backport of PR #6375 as merged into master (eccd909).

What do these changes do?

$sbj.

Are there changes in behavior for the user?

Nope.

Related issue number

N/A

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> for example (588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the pr
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: "Fix issue with non-ascii contents in doctest text files."

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (3.9@7f6c533). Click here to learn what that means.
The diff coverage is n/a.

❗ Current head eccd909 differs from pull request most recent head 0a22ff3. Consider uploading reports for the commit 0a22ff3 to get more accurate results

@@          Coverage Diff           @@
##             3.9    #6377   +/-   ##
======================================
  Coverage       ?   93.33%           
======================================
  Files          ?      104           
  Lines          ?    30403           
  Branches       ?     3063           
======================================
  Hits           ?    28376           
  Misses         ?     1850           
  Partials       ?      177           

Flag	Coverage Δ
unit	93.25% <0.00%> (?)

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