fix: fix proxy unmodified response when body tag is missing

[ndajr]

Based on https://github.com/air-verse/air/pull/604. I found other issues as well, we are missing some returns in case of http internal error responses

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 26.31579% with 14 lines in your changes missing coverage. Please review.

Files	Coverage Δ
runner/proxy.go	67.30% <26.31%> (-7.19%)	:arrow_down:

... and 2 files with indirect coverage changes

[ndajr]

This coverage thing is a bit annoying, by adding returns it thinks the coverage reduced but it's in practise unchanged, we are just fixing the bug. Any ideas on how to fix this or easy ways to improve coverage?