tests: Baseline the protobuf conformance suite per runner release

The failure list has to match conformance_test_runner, whose version is
not ours to pin: CI takes the runner from the /usr/local protobuf and
everything else qtgrpc links from vcpkg. Test names differ between
releases, and the runner rejects a list naming a test it does not have
as loudly as one that fails, so one list cannot serve both.

Name each list after its release, keeping the existing one as
expect_failing_tests_v21.9.txt and adding v33.4 for the vcpkg port. The
release defaults from Protobuf_VERSION, QT_PROTOBUF_CONFORMANCE_VERSION
overrides it where library and runner differ as in CI, and an unknown
release skips the test instead of failing against the wrong baseline.

Two conditions were also missing the $ENV sigil and so always ran.

Always copy the vendored protos. With QT_PROTOBUF_CONFORMANCE_VERSION
naming the runner, QT_ALLOW_DOWNLOAD could only fetch the same 33.4
files from GitHub again, adding a network dependency for nothing.

Drop the 21.9 list and the override once protobuf[conformance] ships the
runner from vcpkg.

Task-number: QTBUG-150055
Pick-to: 6.12
Change-Id: I3b33e0907e6e8e5788b7c32364dff8843ae883ec
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>