fix(package.json): update @graphprotocol/grc-20 dependency to ^0.21.3

Author: marcusrein

package.json

@@ -15,6 +15,7 @@
     "@babel/core": "^7.27.1",
     "@biomejs/biome": "1.9.4",
     "@changesets/cli": "^2.29.3",
+    "@graphprotocol/grc-20": "^0.21.3",
     "babel-plugin-annotate-pure-calls": "^0.5.0",
     "glob": "^11.0.2",
     "pkg-pr-new": "^0.0.43",