Fix pending migration implied by Django 4.0 changes (#634)

[sveetch]

• Added new migration as expected by Django 4.0
• Pinned django-filer>=1.4.0,<2.1 in tests base requirements because it is incompatible with supported Django versions from tox config

I've launched tox on my work and it runned almost well but failed on environments with Django 3.2 because of missing migrations from some dependencies (filer, easy_thumbnails), possibly because of the same bug we are fixing here.

I'm attaching the full tox run output here so you can check yourself without to run it yet:

tox_log_output.txt

Also i'm not totally sure about my migration which have a dependency to the last CMS one, but i saw there is no CMS migration dependency in any of the djangocms-text-ckeditor migrations, maybe you were removing them for a reason, or this is normal, i don't know..

Let me know if you want me to remove it if it is not expected.

[lgtm-com]

This pull request introduces 3 alerts when merging 8c36817 into 3c34d2d - view on LGTM.com

new alerts:

• 2 for Missing call to `__init__` during object initialization
• 1 for `__eq__` not overridden when adding attributes

---

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[codecov]

Codecov Report

Merging #635 (0490f9c) into master (3c34d2d) will decrease coverage by 5.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #635      +/-   ##
==========================================
- Coverage   74.91%   69.86%   -5.06%     
==========================================
  Files          20       16       -4     
  Lines         905      448     -457     
  Branches      128       49      -79     
==========================================
- Hits          678      313     -365     
+ Misses        199      118      -81     
+ Partials       28       17      -11     

Impacted Files	Coverage Δ
...editor/migrations/0005_alter_text_cmsplugin_ptr.py	100.00% <100.00%> (ø)
djangocms_text_ckeditor/cms_plugins.py
djangocms_text_ckeditor/__init__.py
djangocms_text_ckeditor/settings.py
djangocms_text_ckeditor/forms.py
djangocms_text_ckeditor/models.py

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[marksweb]

On a side note, coverage reporting needs to ignore migration files.

[lgtm-com]

This pull request introduces 3 alerts when merging 496b4a8 into 3c34d2d - view on LGTM.com

new alerts:

• 2 for Missing call to `__init__` during object initialization
• 1 for `__eq__` not overridden when adding attributes

---

Heads-up: LGTM.com's PR analysis will be disabled on the 5th of December, and LGTM.com will be shut down ⏻ completely on the 16th of December 2022. Please enable GitHub code scanning, which uses the same CodeQL engine ⚙️ that powers LGTM.com. For more information, please check out our post on the GitHub blog.

[fsbraun]

As a remark: Migration tests are fixed in #631