fix: ensure payload includes up-to-date _img

[danielroe]

• context: fix: allow full usage of $img in plugins #284

I'm not sure why beforeNuxtRender isn't properly setting the page data but this does fix the issue

closes #297

[codecov-commenter]

Codecov Report

Merging #303 (c70ccb6) into main (e71311f) will decrease coverage by 0.30%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #303      +/-   ##
==========================================
- Coverage   58.08%   57.77%   -0.31%     
==========================================
  Files          25       25              
  Lines         563      566       +3     
  Branches      169      170       +1     
==========================================
  Hits          327      327              
- Misses        236      239       +3     

Impacted Files	Coverage Δ
src/runtime/image.ts	67.88% <0.00%> (-1.93%)	⬇️

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