refactor(starter): upgrade to new version of gatsby

internal/testing/__mocks__/gatsby.ts

@@ -0,0 +1,28 @@
+import React from "react";
+
+const gatsby = jest.requireActual("gatsby");
+
+export default {
+  ...gatsby,
+  graphql: jest.fn(),
+  Link: jest
+    .fn()
+    .mockImplementation(
+      ({
+        activeClassName,
+        activeStyle,
+        getProps,
+        innerRef,
+        ref,
+        replace,
+        to,
+        ...rest
+      }) =>
+        React.createElement("a", {
+          ...rest,
+          href: to,
+        }),
+    ),
+  StaticQuery: jest.fn(),
+  useStaticQuery: jest.fn(),
+};