fix: correct ResponseRecorder hijack state tracking

[immanuwell]

Proposed Changes

• fix the inverted hijack state check in ResponseRecorder
• add coverage for failed and successful hijack cases
• keep the later error status intact when hijack fails, this was a small paper cut tbh

Repro

1. Run go test ./pkg/http -run TestResponseRecorder -count=1
2. Before this patch, failed_hijack ends up with 202 instead of 502
3. The same old logic also flips successful_hijack the wrong way, kinda backwards

Release Note

NONE

[knative-prow]

Welcome @immanuwell! It looks like this is your first PR to knative/serving 🎉

[knative-prow]

Hi @immanuwell. Thanks for your PR.

I'm waiting for a knative member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

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[dprotaso]

/ok-to-test

[dprotaso]

/lgtm
/approve

thanks for the fix!

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dprotaso, immanuwell

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.28%. Comparing base (42d556e) to head (de5d30e).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16611      +/-   ##
==========================================
+ Coverage   80.22%   80.28%   +0.05%     
==========================================
  Files         217      217              
  Lines       13568    13568              
==========================================
+ Hits        10885    10893       +8     
+ Misses       2316     2310       -6     
+ Partials      367      365       -2     

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