Fix typo simple XML mod

Author: sophmaca

notebooks/modifications/xml/exercises/xml_timestep_exercise.ipynb

@@ -26,7 +26,7 @@
     "\n",
     "Change the physics timestep in the atmosphere and land to 1200 seconds (default is 1800). Run 5 days.\n",
     "\n",
-    "**Note:** We are using an F-compset (i.e., F1850C_LTso) instead of a B-compset (i.e., F1850C_LTso) for this exercise due to a small namelist bug in the CESM3 tutorial tag. This exercise can be replicated with a B-compset with other versions of CESM. For information on the difference between F and B compsets, see the [CAM challenge introduction section](../../../challenge/cam/cam.ipynb).\n",
+    "**Note:** We are using an F-compset (i.e., F1850C_LTso) instead of a B-compset (i.e., B1850C_LTso) for this exercise due to a small namelist bug in the CESM3 tutorial tag. This exercise can be replicated with a B-compset with other versions of CESM. For information on the difference between F and B compsets, see the [CAM challenge introduction section](../../../challenge/cam/cam.ipynb).\n",
     "    \n",
     "</div>"
    ]