TestE2E/BackendUpgrade/All_requests_must_succeed is flaky

```
=== RUN TestE2E/BackendUpgrade/All_requests_must_succeed
helpers.go:807: 2026-03-05T10:17:42.490474747Z: Conditions matched expectations
helpers.go:807: 2026-03-05T10:17:42.490569193Z: Route gateway-conformance-infra/http-backend-upgrade Parents matched expectations
backend_upgrade.go:47: 2026-03-05T10:17:42.494245667Z: Making GET request to host via http://172.18.0.203/backend-upgrade
http.go:291: 2026-03-05T10:17:42.499088617Z: Request passed
backend_upgrade.go:70: 2026-03-05T10:17:42.503371807Z: Starting load generation
backend_upgrade.go:74: 2026-03-05T10:17:42.503481441Z: Restarting deployment
{"ts":1772705862.503562,"level":"info","r":12050,"file":"utils.go","line":269,"msg":"Log level is now 4 Error (was 2 Info)"}
backend_upgrade.go:77: 2026-03-05T10:17:46.560292351Z: Stopping load generation and collecting results
{"ts":1772705872.558055,"level":"err","r":12194,"file":"http_client.go","line":1137,"msg":"Timeout error (incomplete/invalid response)","err":"read tcp 172.18.0.1:48508->172.18.0.203:80: i/o timeout","size":0,"header_len":0,"dest":{"IP":"172.18.0.203","Port":80,"Zone":""},"url":"http://172.18.0.203/backend-upgrade","thread":32,"run":0}
{"ts":1772705872.563110,"level":"err","r":12195,"file":"http_client.go","line":1137,"msg":"Timeout error (incomplete/invalid response)","err":"read tcp 172.18.0.1:48514->172.18.0.203:80: i/o timeout","size":0,"header_len":0,"dest":{"IP":"172.18.0.203","Port":80,"Zone":""},"url":"http://172.18.0.203/backend-upgrade","thread":33,"run":0}
{"ts":1772705872.565254,"level":"err","r":12162,"file":"http_client.go","line":1137,"msg":"Timeout error (incomplete/invalid response)","err":"read tcp 172.18.0.1:48578->172.18.0.203:80: i/o timeout","size":0,"header_len":0,"dest":{"IP":"172.18.0.203","Port":80,"Zone":""},"url":"http://172.18.0.203/backend-upgrade","thread":0,"run":0}
{"ts":1772705872.566370,"level":"err","r":12185,"file":"http_client.go","line":1137,"msg":"Timeout error (incomplete/invalid response)","err":"read tcp 172.18.0.1:48566->172.18.0.203:80: i/o timeout","size":0,"header_len":0,"dest":{"IP":"172.18.0.203","Port":80,"Zone":""},"url":"http://172.18.0.203/backend-upgrade","thread":23,"run":0}
{"ts":1772705872.570484,"level":"err","r":12200,"file":"http_client.go","line":1137,"msg":"Timeout error (incomplete/invalid response)","err":"read tcp 172.18.0.1:48612->172.18.0.203:80: i/o timeout","size":0,"header_len":0,"dest":{"IP":"172.18.0.203","Port":80,"Zone":""},"url":"http://172.18.0.203/backend-upgrade","thread":38,"run":0}
{"ts":1772705872.570768,"level":"err","r":12179,"file":"http_client.go","line":1137,"msg":"Timeout error (incomplete/invalid response)","err":"read tcp 172.18.0.1:48606->172.18.0.203:80: i/o timeout","size":0,"header_len":0,"dest":{"IP":"172.18.0.203","Port":80,"Zone":""},"url":"http://172.18.0.203/backend-upgrade","thread":17,"run":0}
{"ts":1772705872.571571,"level":"err","r":12204,"file":"http_client.go","line":1137,"msg":"Timeout error (incomplete/invalid response)","err":"read tcp 172.18.0.1:48624->172.18.0.203:80: i/o timeout","size":0,"header_len":0,"dest":{"IP":"172.18.0.203","Port":80,"Zone":""},"url":"http://172.18.0.203/backend-upgrade","thread":42,"run":0}
utils.go:300: 2026-03-05T10:17:52.58703647Z: Load completed after 10.035909196s with 8719 requests, 8712 success, 7 failures and 7 errors
backend_upgrade.go:86: 2026-03-05T10:17:52.587129853Z: Load test failed
```