Summarize XPASS-ing tests in CI

[sgillies]

We're xfailing some tests that have a history of flakiness or timing out, but it's difficult to see when they xpass in the GitHub UI. You have to click through each job, find the step and scroll through it. And we've got a lot of jobs.

I've tried to add a summary job. It's not very fancy (I'm having trouble reproducing some unexpected grep behavior on my laptop), but it does show every xfailing test with information that helps guide us back to the particular job.

For example, this

XPASSes:
test-outputs/partial-test-output-tiledb-3.9-pinned-ubuntu-24.04-2/test.log:tests/taskgraphs/test_server_side.py::ConnectToExistingTest::test_running_graph �[33mXPASS�[0m
test-outputs/partial-test-output-tiledb-3.9-pinned-ubuntu-24.04-2/test.log:=================================== XPASSES ====================================
test-outputs/partial-test-output-tiledb-3.9-pinned-ubuntu-24.04-2/test.log:�[33mXPASS�[0m tests/taskgraphs/test_server_side.py::�[1mConnectToExistingTest::test_running_graph�[0m - Server side error, graph not computed in expected time.
test-outputs/partial-test-output-tiledb-3.9-pinned-ubuntu-24.04-4/test.log:tests/test_dag.py::DAGClassTest::test_resource_class �[33mXPASS�[0m (Requires...)
test-outputs/partial-test-output-tiledb-3.9-pinned-ubuntu-24.04-4/test.log:=================================== XPASSES ====================================
test-outputs/partial-test-output-tiledb-3.9-pinned-ubuntu-24.04-4/test.log:�[33mXPASS�[0m tests/test_dag.py::�[1mDAGClassTest::test_resource_class�[0m - Requires resolution of upstream issue.

tells us that two tests unexpectedly passed. Both with Python 3.9 (the Python 3.12 tests don't exercise UDFs or task graphs), pinned dependencies. One test is part 2 of the batch of splits, one in part 4.

In the UI, it looks like this:

The history of this PR is a mess. The net changes are small.

[sgillies]

I've been unable to get "^XPASS" to work as a pattern, neither with nor without --extended-regexp. In the GHA runner, it matches nothing.