Fix unused variable lint error in useInkBleed test

Prefix 'run' with underscore in cancel() test case where the
start() return value is intentionally unused -- cancel() does not
take a run token, unlike finish().

Author: Chris0Jeky

frontend/taskdeck-web/src/tests/components/paper/useInkBleed.spec.ts

@@ -165,7 +165,7 @@ describe('useInkBleed', () => {
 
   it('cancel() clears state without firing done', () => {
     const { exposed } = createHost()
-    const run = exposed.bleed.start()
+    const _run = exposed.bleed.start()
     vi.advanceTimersByTime(1000)
 
     exposed.bleed.cancel()