Do not allow reopening of closed events

[johannaengland]

Might close #188 (depending on if changing closed events should be allowed or not).

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.86%. Comparing base (09dbdd9) to head (c6be42d).

:exclamation: Current head c6be42d differs from pull request most recent head c8a0843. Consider uploading reports for the commit c8a0843 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #201 +/- ## ======================================= Coverage 98.86% 98.86% ======================================= Files 41 41 Lines 5422 5429 +7 ======================================= + Hits 5360 5367 +7 Misses 62 62 ```

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[github-actions[bot]]

Test results

    3 files      3 suites   32s :stopwatch: 290 tests 290 :heavy_check_mark: 0 :zzz: 0 :x: 870 runs  868 :heavy_check_mark: 2 :zzz: 0 :x:

Results for commit c8a08435.

:recycle: This comment has been updated with latest results.

[johannaengland]

I would like to wait for a review from @lunkwill42 before merging, mainly for the design decision if this is enough to close #188.

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud