test: robuster http2-large-file test
This makes sure the first request is not sent before the client is ready to respond. Therefore the ECONNRESET errors should be resolved.
Fixes: #22327 (closed)
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines