t5559-http-fetch-smart-http2 failures

Hi,

I started seeing failures in rc0 but I was distracted by the long weekend.

The changes in 73c49a4474 (t: run t5551 tests with both HTTP and HTTP/2, 2022-11-11) seem to rather frequently trigger test failures on Fedora.

The most frequent test to fail is "large fetch-pack requests can be sent using chunked encoding" (t5559.30), but earlier tests have also failed on occasion. For the common failure, the test exits with:

    expecting success of 5559.30 'large fetch-pack requests can be sent using chunked encoding': 
	    GIT_TRACE_CURL=true git -c http.postbuffer=65536 \
		    clone --bare "$HTTPD_URL/smart/repo.git" split.git 2>err &&
	    {
		    test_have_prereq HTTP2 ||
		    grep "^=> Send header: Transfer-Encoding: chunked" err
	    }
    +++ GIT_TRACE_CURL=true
    +++ git -c http.postbuffer=65536 clone --bare http://127.0.0.1:5559/smart/repo.git split.git
    error: last command exited with $?=128
    not ok 30 - large fetch-pack requests can be sent using chunked encoding

(Less frequently, I've seen the last command exit 141.)

I haven't been able to track down the problem, which happens a lot on the Fedora build system but less often during local builds. Obviously, the bug is too shy to show itself while anyone is watching. ;)

I can easily disable the failing tests for a bit, but does anyone have an idea what might be the cause or how to better debug it when it occurs on a buildsystem without direct access?

Thanks,