Fix bundle/05_spleen_segmentation_lightning: upgrade pytorch-lightning pin

pytorch-lightning~=2.0.0 (2.0.9) imports mlflow at module level via
pytorch_lightning.loggers.mlflow; mlflow 3.13.0 fails to initialize
under Python 3.12, making `import pytorch_lightning` fail in the
training subprocess.

pytorch-lightning>=2.1 uses lazy mlflow imports; confirmed working
with 2.6.5: training and evaluation run to completion.

Also documents the root cause in diagnose_1_6_release.md: two-part
R7 issue (fd-limit download truncation + mlflow/pl import chain).

Author: garciadias

bundle/05_spleen_segmentation_lightning.ipynb

@@ -38,7 +38,7 @@
    "outputs": [],
    "source": [
     "!python -c \"import monai\" || pip install -q \"monai-weekly[ignite,pyyaml]\"\n",
-    "!pip install -q pytorch-lightning~=2.0.0"
+    "!pip install -q pytorch-lightning>=2.1"
    ]
   },
   {
@@ -855,7 +855,7 @@
    "execution_count": 11,
    "id": "c5ba337d-a5b0-47de-9ae2-1554a2cb4f86",
    "metadata": {},
-    "outputs": [
+   "outputs": [
     {
      "name": "stdout",
      "output_type": "stream",