fix: use correct attribute selector for stylesheet link check

Agent-Logs-Url: https://github.com/nextcloud/unsplash/sessions/e614a94e-a2a4-4aa3-bbc2-6cac574430f9

Co-authored-by: skjnldsv <14975046+skjnldsv@users.noreply.github.com>

Author: Copilot

playwright/e2e/login-background.spec.ts

@@ -11,9 +11,7 @@ test.describe('Login page background', () => {
 
 		// The BeforeTemplateRenderedEventListener injects a <link> pointing to
 		// the unsplash CSS endpoint when the login style is enabled (default).
-		const link = page.locator('link[rel="stylesheet"]').filter({
-			has: page.locator('[href*="/apps/unsplash/api/login.css"]'),
-		})
+		const link = page.locator('link[rel="stylesheet"][href*="/apps/unsplash/api/login.css"]')
 		await expect(link).toHaveCount(1)
 	})