@uppy/companion: fix deploy Yarn version (transloadit#3327)

* @uppy/companion: fix deploy

When running from the Dockerfile, Corepack cannot pick up the
information from the parent package.json and tries to run with an
older version of Yarn.

* Update update-yarn.sh

package.json

@@ -112,7 +112,9 @@
     "test": "bash -c 'source env.test.sh && ../../../node_modules/jest/bin/jest.js'",
     "test:watch": "yarn test -- --watch"
   },
+  "packageManager": "yarn@3.1.0",
   "engines": {
-    "node": ">=10.20.1"
+    "node": ">=10.20.1",
+    "yarn": "3.1.0"
   }
 }