Call super().clean instead of accessing self.cleaned_data directly

[atombrella]

Not sure what the motivation for not calling clean, but you're missing out on all of django's built-in validation.

[codecov]

Codecov Report

Merging #717 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #717      +/-   ##
==========================================
+ Coverage   69.95%   69.97%   +0.02%     
==========================================
  Files          89       89              
  Lines        4423     4426       +3     
==========================================
+ Hits         3094     3097       +3     
  Misses       1329     1329

Impacted Files	Coverage Δ
src/wiki/forms.py	63.71% <100%> (+0.2%)	⬆️
src/wiki/plugins/attachments/forms.py	63.71% <100%> (+0.32%)	⬆️

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[benjaoming]

Oh woops, bad mistake, could cause issues.

[benjaoming]

Seeing 100% diff coverage and that tests are fine would indicate that none of these were intentional in leaving out super()