Catch ValueError due to approximate date with no day

[amakarudze]

If an existing organizer applies to organize an event while their old event application had an approximate date with month and year only, validation fails because the day which will be will be out of range for that month. This PR fixes #885

Changes in this PR

• Add try...except block to the event application validation and catch the ValueError.
• Add test for event application years apart.
• Add test for old event application with only an approximate date with month and year only.

[codecov-commenter]

Codecov Report

Merging #887 (4979903) into main (a858d59) will decrease coverage by 0.01%.
The diff coverage is 71.42%.

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@@            Coverage Diff             @@
##             main     #887      +/-   ##
==========================================
- Coverage   80.28%   80.27%   -0.01%     
==========================================
  Files          95       95              
  Lines        2845     2849       +4     
  Branches      273      274       +1     
==========================================
+ Hits         2284     2287       +3     
- Misses        503      504       +1     
  Partials       58       58              

Impacted Files	Coverage Δ
organize/models.py	90.15% <71.42%> (-0.48%)	⬇️

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[marksweb]

In terms of the test data, this looks good. I've just got a couple of points.

And sorry this took so long. I just found this review request at the end of my notifications.

[marksweb]

LGTM 👍