update to 2.39.0-rc0
    
    Add mod_http2 BuildRequires for t5559-http-fetch-smart-http2; skip it on
    EL7, which lacks it.  Ignore the expected 'missing HTTP2' output from
    t5551-http-fetch-smart.  Use a strict pattern to avoid unintended
    matches.
    
    Sadly, we must also disable t5559 for now.  It fails very often across
    all architectures.  The most common failure is "large fetch-pack
    requests can be sent using chunked encoding" (t5559.30), but earlier
    tests have also failed.  Until these failures are understood and
    resolved, the entire test is disabled globally.  (It's also disabled for
    EL-7, which is redundant now but won't be after we re-enable the test
    globally in the near future.)
    
    We can't simply skip the mod_http2 dependency here because we set
    GIT_TEST_HTTPD=true.  Per upstream 73c49a4474 (t: run t5551 tests with
    both HTTP and HTTP/2, 2022-11-11):
    
        If HTTP/2 isn't supported on a given platform, then t5559 should
        bail during the webserver setup, and gracefully skip all tests
        (unless GIT_TEST_HTTPD has been changed from "auto" to "yes", where
        the point is to complain when webserver setup fails).
    
    Also ignore the 'missing BUILTIN_TXT_$builtin' output which comes from
    upstream a0c3244796 (doc SYNOPSIS & -h: use "-" to separate words in
    labels, not "_", 2022-10-13).  We may want to loosen this in the future,
    but for now ignore it because it doesn't help us identify missing test
    dependencies.
    
    Release notes:
    https://github.com/git/git/raw/v2.39.0-rc0/Documentation/RelNotes/2.39.0.txt