Add a small jest mock for addLabels. Not used.

__mocks__/@actions/github.ts

@@ -13,7 +13,13 @@ export const context = {
 const mockApi = {
   rest: {
     issues: {
-      addLabels: jest.fn(),
+      addLabels: jest.fn(({ owner, repo, issue_number, labels }) =>
+        Promise.resolve({
+          data: labels.map((l) => {
+            name: l;
+          }),
+        })
+      ),
       removeLabel: jest.fn(),
     },
     pulls: {