feat: if seed peer download task, return NeedBackToSource directly

[gaius-qi]

Description

Related Issue

Motivation and Context

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation Update (if none of the other choices apply)

Checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (5989a4d) 51.10% compared to head (75ea1ff) 51.08%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2980      +/-   ##
==========================================
- Coverage   51.10%   51.08%   -0.02%     
==========================================
  Files         161      161              
  Lines       21894    21894              
==========================================
- Hits        11189    11185       -4     
- Misses      10045    10047       +2     
- Partials      660      662       +2     

Flag	Coverage Δ
Object-compatibility-e2etests	?
e2etests	?
unittests	51.08% <100.00%> (-0.02%)	⬇️

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Files	Coverage Δ
scheduler/service/service_v2.go	84.85% <100.00%> (ø)

... and 2 files with indirect coverage changes