chore(deps): update dependency pngjs to v6 (#556)

Author: renovate-bot

packages/google-privacy-dlp/samples/package.json

@@ -24,7 +24,7 @@
     "chai": "^4.2.0",
     "mocha": "^8.0.0",
     "pixelmatch": "^5.0.0",
-    "pngjs": "^5.0.0",
+    "pngjs": "^6.0.0",
     "uuid": "^8.0.0"
   }
 }