chore(deps): update upm project dependency com.unity.timeline to v1.8.8

Author: unity-renovate[bot]

testproject/Packages/manifest.json

@@ -14,7 +14,7 @@
     "com.unity.test-framework": "1.3.3",
     "com.unity.test-framework.performance": "2.8.1-preview",
     "com.unity.textmeshpro": "3.0.6",
-    "com.unity.timeline": "1.8.2",
+    "com.unity.timeline": "1.8.8",
     "com.unity.ugui": "1.0.0",
     "com.unity.modules.ai": "1.0.0",
     "com.unity.modules.androidjni": "1.0.0",