Fix raising ValidationError in validate_email_address

[sumandari]

Please see #1372.

There was return 500 when user updated information in Update Sustaining Member page. After replicated the issue, I found that fixing the way we raise ValidationError in validate_email_address will resolve this issue

[codecov[bot]]

Codecov Report

Merging #1376 (f4b45d3) into develop (bfab4ac) will increase coverage by 0.06%. The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop    #1376      +/-   ##
===========================================
+ Coverage    64.29%   64.35%   +0.06%     
===========================================
  Files          180      180              
  Lines         9664     9664              
  Branches       758      758              
===========================================
+ Hits          6213     6219       +6     
+ Misses        3207     3201       -6     
  Partials       244      244              

Impacted Files	Coverage Δ
...ct/certification/models/certifying_organisation.py	96.25% <100.00%> (+2.50%)	:arrow_up:
django_project/changes/models/sponsor.py	91.35% <100.00%> (+4.93%)	:arrow_up:

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[timlinux]

LGTM