fix(routes/api): handle non websocket connection

routes/api/serviceworker/is-online.tsx

@@ -2,6 +2,15 @@ import { define } from '../../../utils.ts'
 
 export const handler = define.handlers({
 	GET(ctx) {
+		if (
+			ctx.req.headers.get('connection') !== 'Upgrade' &&
+			ctx.req.headers.get('upgrade') !== 'websocket'
+		) {
+			return new Response('Request is not a websocket upgrade.', {
+				status: 400,
+			})
+		}
+
 		const { response } = Deno.upgradeWebSocket(ctx.req)
 		ctx.state.skipMiddlewares = true
 		return response