fix(vue-renderer): prevent can't set headers after they are sent

[pi0]

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Description

Prevent "Can't set headers after they are sent" error for modern server mode

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly. (PR: #)
• I have added tests to cover my changes (if not applicable, please state why)
• All new and existing tests are passing.

[codecov-io]

Codecov Report

Merging #5863 into dev will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              dev    #5863      +/-   ##
==========================================
- Coverage   95.72%   95.72%   -0.01%     
==========================================
  Files          82       82              
  Lines        2690     2689       -1     
  Branches      690      690              
==========================================
- Hits         2575     2574       -1     
  Misses         97       97              
  Partials       18       18

Flag	Coverage Δ
#e2e	100% <ø> (ø)	⬆️
#fixtures	50.39% <0%> (+0.01%)	⬆️
#unit	92.71% <100%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
packages/vue-renderer/src/renderers/modern.js	98.3% <100%> (-0.03%)	⬇️

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