Bundle dependency PRs on a bi-weekly basis

[sliverc]

Currently pyup causes a lot of noise so when looking at the closed
PR the real PRs can be easily overlooked.
As we only have test dependencies simply updating on a bi-weekly basis
should be sufficient.

Description of the Change

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 #757 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #757      +/-   ##
==========================================
+ Coverage   97.08%   97.12%   +0.03%     
==========================================
  Files          54       54              
  Lines        2742     2779      +37     
==========================================
+ Hits         2662     2699      +37     
  Misses         80       80

Impacted Files	Coverage Δ
rest_framework_json_api/renderers.py	87.05% <ø> (+0.25%)	⬆️
example/api/resources/identity.py	100% <ø> (ø)	⬆️
example/tests/test_model_viewsets.py	100% <ø> (ø)	⬆️
example/tests/test_format_keys.py	100% <ø> (ø)	⬆️
example/tests/test_sideload_resources.py	100% <ø> (ø)	⬆️
rest_framework_json_api/metadata.py	91.66% <100%> (ø)	⬆️
rest_framework_json_api/relations.py	87.31% <100%> (+0.12%)	⬆️
rest_framework_json_api/exceptions.py	84.61% <100%> (ø)	⬆️
example/factories.py	100% <0%> (ø)	⬆️
example/tests/conftest.py	100% <0%> (ø)	⬆️
... and 13 more

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[n2ygk]

@sliverc Sorry, I just noticed these review requests. I've been busy with work/life imbalance. I'll try to get to these in the next week or so.

[n2ygk]

LGTM - sorry for the delay in reviewing