Run UI tests on webkit

[jtpio]

References

Investigate #944

Code changes

Run UI tests on webkit to catch potential issues with Safari.

• Add webkit to the test matrix
• Add webkit reference snapshots

User-facing changes

TBD

Backwards-incompatible changes

None

[github-actions]

👈 Try it on ReadTheDocs

[jtpio]

At least the setImmediate issue mentioned in #944 is reproducible on CI:

[jtpio]

So the "Basic code execution" test seems to be passing:

Which is about executing the JavaScript notebook, with the JavaScript kernel also running in a web worker:

jupyterlite/ui-tests/test/kernels.spec.ts

Lines 15 to 24 in da9e985

	test('Basic code execution', async ({ page }) => {
	await page.goto('lab/index.html');
	const name = 'javascript.ipynb';
	await page.filebrowser.open(name);
	await page.notebook.run();
	await page.notebook.save();
	const output = await page.notebook.getCellTextOutput(2);
	expect(output).toBeTruthy();
	});

So maybe the setImmediate issue is only for the Pyodide kernel. We can check if that also happens with the Xeus Python kernel on webkit to narrow it down more.

[jtpio]

For reference the PR to test jupyterlite-xeus-python on webkit: jupyterlite/xeus-python-kernel#175