Remove cronjob for prepare-release workflow

[bugarela]

Hello

We have this cronjob preparing a release every Monday, but it doesn't make sense anymore as there isn't a continuous flow of changes to this project currently. It is annoying because it creates a branch for the next release, and whenever I actually want to cut a release, the branch is already taken and it errors out - or something like that - and I have to remember to close the bot's PR and delete it's branch.

This simply removes that cronjob. We can easily add it back if it starts making sense again.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.89%. Comparing base (99b93bb) to head (67d9e81).

❗ Current head 67d9e81 differs from pull request most recent head 1030a14. Consider uploading reports for the commit 1030a14 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2894      +/-   ##
==========================================
- Coverage   78.90%   78.89%   -0.02%     
==========================================
  Files         467      467              
  Lines       15975    15975              
  Branches     2556     2556              
==========================================
- Hits        12605    12603       -2     
- Misses       3370     3372       +2     

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[p-offtermatt]

Good change for now! Maybe it needs to be added back in the future :)