allow sequence types for fields with requires (can be empty)

[tclose]

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Summary

Allows task fields of Sequence type to have non-empty requires (as they can be empty if requirements are not met)

Checklist

• I have added tests to cover my changes (if necessary)
• I have updated documentation (if necessary)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 87.89%. Comparing base (47c3958) to head (3af9d53).

Files with missing lines	Patch %	Lines
pydra/compose/base/field.py	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #827   +/-   ##
=======================================
  Coverage   87.89%   87.89%           
=======================================
  Files          84       84           
  Lines       17890    17890           
  Branches     3483     3483           
=======================================
  Hits        15725    15725           
  Misses       1809     1809           
  Partials      356      356           

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