Fix i18n issues in models

[int-y1]

How these i18n issues were detected:

from django.core.management.base import BaseCommand
from django.utils.translation import gettext_lazy as _

from django.apps import apps


class Command(BaseCommand):
    help = 'get all fields missing verbose_name'

    def handle(self, *args, **options):
        goodtype = type(_('yes'))
        for model in apps.get_models():
            if not model._meta.db_table.startswith('judge_'):
                continue
            msg = []
            # meta verbose_name
            if type(model._meta.verbose_name) != goodtype:
                msg.append('class verbose_name')
            if type(model._meta.verbose_name_plural) != goodtype:
                msg.append('class verbose_name_plural')
            # field verbose_name
            for field in model._meta.get_fields():
                if not hasattr(field, 'verbose_name'):
                    continue
                if field.name == 'id':
                    continue
                if type(field._verbose_name) != goodtype:
                    msg.append(f'{type(field._verbose_name)} {field.name}')
            # done
            if msg:
                print(model)
                for s in msg:
                    print(s)
                print()

This still outputs some i18n issues, but I couldn't find them in the frontend.

[codecov-commenter]

Codecov Report

Merging #1910 (9699f2d) into master (0191c77) will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1910      +/-   ##
==========================================
+ Coverage   46.35%   46.40%   +0.05%     
==========================================
  Files         234      234              
  Lines       13089    13103      +14     
==========================================
+ Hits         6067     6081      +14     
  Misses       7022     7022              

Impacted Files	Coverage Δ
judge/admin/problem.py	56.49% <100.00%> (ø)
judge/models/comment.py	39.61% <100.00%> (+0.79%)	⬆️
judge/models/contest.py	96.20% <100.00%> (ø)
judge/models/problem.py	89.26% <100.00%> (+0.09%)	⬆️
judge/models/profile.py	81.97% <100.00%> (ø)
judge/models/runtime.py	70.79% <100.00%> (ø)
judge/models/submission.py	90.50% <100.00%> (+0.18%)	⬆️
judge/models/ticket.py	100.00% <100.00%> (ø)

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