Port tst_QQmlXmlListModel::headers() to QHttpHeadersHEADdev

The test captured outgoing request headers into a QVariantMap keyed by
the raw header name and looked up the Accept header via lowercase
"accept".

Since qtbase/f6b1744b54e7883550c56daa508039061813f790, QHttpHeaders
stores well-known header names in their canonical IANA form, so
QNetworkRequest::rawHeaderList() now returns "Accept" rather than
"accept", so the lowercase lookup and therefore the test failed.

To fix, capture QNetworkRequest::headers() directly and query the
well-known Accept header via the QHttpHeaders API, which is
case-insensitive and no longer depends on the on-the-wire spelling of
the header name.

This way, the code works independent of the QtNetwork change,
unblocking module updates, and avoiding ping-pong string changes in
the future.

Test failure analysis, test fix, and commit message draft by Claude
Opus 4.8.

Amends 828b823938395d4d43f9b7a1b7f53f10a4a6b99b (6.8).

Pick-to: 6.12 6.11 6.8
Change-Id: Id37b3858551533086604ee6bf435aa13bd5d238a
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

0 files changed, 0 insertions, 0 deletions