chore: explicitly add devDependencies for monorepo peerDependencies (#2808)

packages/medusa-plugin-restock-notification/package.json

@@ -17,6 +17,7 @@
     "babel-preset-medusa-package": "^1.1.19",
     "cross-env": "^5.2.1",
     "jest": "^25.5.2",
+    "medusa-interfaces": "^1.3.3",
     "medusa-test-utils": "^1.1.37",
     "pg": "^8.5.1",
     "ulid": "^2.3.0"