Use required attribute from field when getting schema fields

[gmuj]

No description provided.

[codecov-io]

Codecov Report

Merging #766 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #766   +/-   ##
========================================
  Coverage    98.11%   98.11%           
========================================
  Files           15       15           
  Lines         1117     1117           
========================================
  Hits          1096     1096           
  Misses          21       21

Impacted Files	Coverage Δ
django_filters/rest_framework/backends.py	92.85% <ø> (ø)	⬆️

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