bug(web): `permissions policy violation error: unload is not allowed in this document.`

[mcdurdin]

[Violation] Permissions policy violation: unload is not allowed in this document.
(anonymous)	@	bundle.min.js:2
(anonymous)	@	bundle.min.js:2
attachDOMEvent	@	domEventTracker.ts:61
attachHandlers	@	pageIntegrationHandlers.ts:206
constructor	@	pageIntegrationHandlers.ts:46
(anonymous)	@	keymanEngine.ts:222
fulfilled	@	keymanweb.js:69
Promise.then		
step	@	keymanweb.js:81
fulfilled	@	keymanweb.js:69
Promise.then		
step	@	keymanweb.js:81
(anonymous)	@	keymanweb.js:82
__async	@	keymanweb.js:66
init	@	keymanEngine.ts:163
(anonymous)	@	test.js:52

19.0.269-alpha-local, in Keyman Developer Server running locally, on http://localhost:8008