test(backend/e2e): fix /private/explore/pin/:noteAlias forbidden alias test

The test checked the wrong error code, that was thrown because we don't provide the correct request body. The test never failed because of the forbidden alias

Signed-off-by: Philip Molares <philip.molares@udo.edu>

backend/test/private-api/private-api.explore.e2e-spec.ts

@@ -432,8 +432,12 @@ describe('Explore', () => {
     it('throws error if note is forbidden', async () => {
       await agentUser1
         .put(`${PRIVATE_API_PREFIX}/explore/pin/${forbiddenAlias}`)
+        .set('Content-Type', 'application/json')
+        .send({
+          isPinned: true,
+        })
         .expect('Content-Type', /json/)
-        .expect(400);
+        .expect(403);
     });
   });
 });