Block start time editing for started tasks

[aleksfl]

Scope and purpose

Fixes #1900.

Contributor Checklist

Every pull request should have this checklist filled out, no matter how small it is.
More information about contributing to Argus can be found in the
Development docs.

• Added a changelog fragment for towncrier
• Added/amended tests for new/changed code
• Linted/formatted the code with ruff and djLint, easiest by using pre-commit
• The first line of the commit message continues the sentence "If applied, this commit will ...", starts with a capital letter, does not end with punctuation and is 50 characters or less long. See our how-to

[github-actions]

Test results

    6 files  1 188 suites   2m 17s ⏱️
  869 tests   868 ✅ 1 💤 0 ❌
5 214 runs  5 208 ✅ 6 💤 0 ❌

Results for commit c8c9d66.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.21%. Comparing base (b7a7170) to head (c8c9d66).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1909   +/-   ##
=======================================
  Coverage   88.21%   88.21%           
=======================================
  Files         140      140           
  Lines        6848     6850    +2     
=======================================
+ Hits         6041     6043    +2     
  Misses        807      807           

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud