[Fixes #12988] Metadata editor: fix jsonschema caching mechanism

[etj]

Checklist

Reviewing is a process done by project maintainers, mostly on a volunteer basis. We try to keep the overhead as small as possible and appreciate if you help us to do so by completing the following items. Feel free to ask in a comment if you have troubles with any of them.

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• There is a ticket in https://github.com/GeoNode/geonode/issues describing the issue/improvement/feature (a notable exemption is, changes not visible to end-users)
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• New unit tests have been added covering the changes, unless there is an explanation on why the tests are not necessary/implemented
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[codecov]

Codecov Report

Attention: Patch coverage is 56.09756% with 18 lines in your changes missing coverage. Please review.

Project coverage is 67.97%. Comparing base (f0f9e7d) to head (187ce4b).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #12989      +/-   ##
==========================================
- Coverage   67.98%   67.97%   -0.01%     
==========================================
  Files         980      980              
  Lines       59229    59246      +17     
  Branches     6920     6922       +2     
==========================================
+ Hits        40264    40272       +8     
- Misses      17320    17328       +8     
- Partials     1645     1646       +1     

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