Make email validation same or stricter as Django

[raphaelm]

No description provided.

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (e46edf4) 25.53% compared to head (0ec3db5) 25.86%.
Report is 1 commits behind head on master.

Files	Patch %	Lines
...main/java/eu/pretix/libpretixsync/api/PretixApi.kt	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #36      +/-   ##
============================================
+ Coverage     25.53%   25.86%   +0.32%     
- Complexity      388      399      +11     
============================================
  Files           105      106       +1     
  Lines          5905     5927      +22     
  Branches       1034     1037       +3     
============================================
+ Hits           1508     1533      +25     
+ Misses         4155     4153       -2     
+ Partials        242      241       -1     

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