adding another missing package dependency

Packages/manifest.json

     "com.unity.ide.visualstudio": "2.0.2",
     "com.unity.ide.vscode": "1.2.1",
     "com.unity.multiplayer.mlapi": "https://github.com/Unity-Technologies/com.unity.multiplayer.mlapi.git?path=/com.unity.multiplayer.mlapi#develop",
+    "com.unity.postprocessing": "2.3.0",
     "com.unity.test-framework": "1.1.16",
     "com.unity.textmeshpro": "3.0.1",
     "com.unity.timeline": "1.4.3",

Packages/packages-lock.json

       "dependencies": {},
       "url": "https://packages.unity.com"
     },
+    "com.unity.postprocessing": {
+      "version": "2.3.0",
+      "depth": 0,
+      "source": "registry",
+      "dependencies": {},
+      "url": "https://packages.unity.com"
+    },
     "com.unity.test-framework": {
       "version": "1.1.16",
       "depth": 0,