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 88.78%. Comparing base (058d793) to head (28801a2).

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   88.76%   88.78%   +0.02%     
==========================================
  Files          84       84              
  Lines       17890    17890              
  Branches     3483     3483              
==========================================
+ Hits        15880    15884       +4     
+ Misses       1640     1636       -4     
  Partials      370      370              

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