Fix max_epochs not replaced correctly issue (Project-MONAI#1882)

### Checks
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [ ] Avoid including large-size files in the PR.
- [ ] Clean up long text outputs from code cells in the notebook.
- [ ] For security purposes, please check the contents and remove any
sensitive info such as user names and private key.
- [ ] Ensure (1) hyperlinks and markdown anchors are working (2) use
relative paths for tutorial repo files (3) put figure and graphs in the
`./figure` folder
- [ ] Notebook runs automatically `./runner.sh -t <path to .ipynb file>`

---------

Signed-off-by: YunLiu <55491388+KumoLiu@users.noreply.github.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

generation/2d_diffusion_autoencoder/2d_diffusion_autoencoder_tutorial.ipynb

@@ -474,9 +474,8 @@
     }
    ],
    "source": [
-    "max_epochs = (\n",
-    "    1000  # training for longer (1e4 ~ 3h) helps a lot with reconstruction quality, even if the loss is already low\n",
-    ")\n",
+    "# training for longer (1e4 ~ 3h) helps a lot with reconstruction quality, even if the loss is already low\n",
+    "max_epochs = 1000\n",
     "val_interval = 100\n",
     "print_interval = 50\n",
     "iter_loss_list, val_iter_loss_list = [], []\n",