Drop node 12

And embrace Node 18

See https://nodejs.org/en/about/releases/

Author: mroderick

.github/workflows/main.yml

@@ -143,7 +143,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [12, 14, 16]
+        node-version: [14, 16, 18]
 
     steps:
       - uses: actions/checkout@v2

lib/sinon/default-behaviors.js

@@ -269,6 +269,7 @@ var defaultBehaviors = {
         Object.defineProperty(rootStub.rootObj, rootStub.propName, {
             value: newVal,
             enumerable: true,
+            writable: true,
             configurable:
                 rootStub.shadowsPropOnPrototype ||
                 isPropertyConfigurable(rootStub.rootObj, rootStub.propName),