Convert HyperlinkedRelatedField tests to pytest style

[sliverc]

Related to #468

Description of the Change

Continuation of tests conversion

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 #889 (22ca7c7) into master (1de9d18) will decrease coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #889      +/-   ##
==========================================
- Coverage   97.73%   97.70%   -0.04%     
==========================================
  Files          60       59       -1     
  Lines        3269     3182      -87     
==========================================
- Hits         3195     3109      -86     
+ Misses         74       73       -1     

Impacted Files	Coverage Δ
tests/conftest.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1de9d18...e58ea7a. Read the comment docs.

[sliverc]

@n2ygk Do you think you will find time to look at this PR?

[n2ygk]

LGTM