[Automated] Update net-gateway-api nightly

[knative-automation]

/assign @knative/serving-writers /cc @knative/serving-writers

Produced via:

for x in net-gateway-api.yaml istio-gateway.yaml contour-gateway.yaml gateway-api.yaml; do
  curl https://storage.googleapis.com/knative-nightly/net-gateway-api/latest/$x > ${GITHUB_WORKSPACE}/./third_party/gateway-api-latest/$x
done

Details:

bumping knative.dev/net-gateway-api 81d8531...8aa9d20:
  > 8aa9d20 upgrade to latest dependencies (# 760)

[knative-prow[bot]]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 84.54%. Comparing base (3ae5a0e) to head (97e0987). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #15448 +/- ## ========================================== + Coverage 84.49% 84.54% +0.05% ========================================== Files 219 219 Lines 13605 13605 ========================================== + Hits 11496 11503 +7 + Misses 1738 1733 -5 + Partials 371 369 -2 ```

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[ReToCode]

/retest