Remove global ignore of serializer warnings

[sliverc]

Description of the Change

Deprecation warnings should not be suppressed globally but instead test code be adjusted to new default behavior.

Cleanup of #776

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[codecov]

Codecov Report

Merging #816 into master will decrease coverage by 0.44%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #816      +/-   ##
==========================================
- Coverage   97.52%   97.08%   -0.45%     
==========================================
  Files          58       58              
  Lines        3157     3158       +1     
==========================================
- Hits         3079     3066      -13     
- Misses         78       92      +14     

Impacted Files	Coverage Δ
example/tests/integration/test_meta.py	100.00% <ø> (ø)
.../tests/integration/test_non_paginated_responses.py	100.00% <ø> (ø)
example/tests/integration/test_pagination.py	100.00% <ø> (ø)
example/tests/test_filters.py	100.00% <ø> (ø)
example/tests/test_views.py	100.00% <ø> (ø)
example/tests/unit/test_default_drf_serializers.py	100.00% <ø> (ø)
example/settings/dev.py	100.00% <100.00%> (ø)
example/tests/test_serializers.py	100.00% <100.00%> (ø)
rest_framework_json_api/renderers.py	83.07% <0.00%> (-4.39%)	⬇️

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[n2ygk]

Looks good. Thanks.