fix: Mark site update doc as cancelled when cancelling an update rather than deleting it

[phot0n]

• probably dont allow editing a scheduled update if it has been cancelled? (check siteupdatedialog.vue) -- there is a check for status to be scheduled so it should be fine for the most part i guess

[codecov]

Codecov Report

❌ Patch coverage is 35.29412% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.89%. Comparing base (76f69ad) to head (132d6da).
⚠️ Report is 11 commits behind head on develop.

Files with missing lines	Patch %	Lines
press/press/doctype/site_update/site_update.py	33.33%	10 Missing ⚠️
press/press/doctype/site/site.py	50.00%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (35.29%) is below the target coverage (75.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4123      +/-   ##
===========================================
- Coverage    44.89%   44.89%   -0.01%     
===========================================
  Files          726      725       -1     
  Lines        49737    49738       +1     
===========================================
- Hits         22331    22330       -1     
- Misses       27406    27408       +2     

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[phot0n]

a bit unsure about things like:

https://github.com/frappe/press/blob/develop/press/press/doctype/site_update/site_update.py#L453-L462

and

https://github.com/frappe/press/blob/develop/press/press/doctype/site_update/site_update.py#L893-L901

these dont have a filter for status