dev: add test-dev command for easier testing of packages (#2627)

@si14 you might know a better way to wire this up! lemme know if there's
something more clever here.

### Change Type

- [x] `internal` — Any other changes that don't affect the published
package[^2]

### Release Notes

- Adds easier testing command for individual packages.

apps/dotcom-asset-upload/package.json

@@ -11,6 +11,7 @@
 	"scripts": {
 		"dev": "cross-env NODE_ENV=development wrangler dev --log-level info --persist-to tmp-assets",
 		"test": "lazy inherit --passWithNoTests",
+		"test-dev": "yarn run -T jest --watch",
 		"test-coverage": "lazy inherit --passWithNoTests",
 		"lint": "yarn run -T tsx ../../scripts/lint.ts"
 	},