doc: fix typo in concentration description in notebook (#5284)

* Fix typo in concentration description in notebook

* Add CHANGELOG.md entry for typo fix

* Remove unneccesary changelog entry

Co-authored-by: Agriya Khetarpal <[email protected]>

---------

Co-authored-by: Agriya Khetarpal <[email protected]>

Author: gregordecristoforo

docs/source/examples/notebooks/creating_models/4-comparing-full-and-reduced-order-models.ipynb

@@ -24,7 +24,7 @@
     "$$\n",
     "\\left.c\\right\\vert_{t=0} = c_0,\n",
     "$$\n",
-    "where $c$$ is the concentration, $r$ the radial coordinate, $t$ time, $R$ the particle radius, $D$ the diffusion coefficient, $j$ the interfacial current density, $F$ Faraday's constant, and $c_0$ the initial concentration. \n",
+    "where $c$ is the concentration, $r$ the radial coordinate, $t$ time, $R$ the particle radius, $D$ the diffusion coefficient, $j$ the interfacial current density, $F$ Faraday's constant, and $c_0$ the initial concentration. \n",
     "\n",
     "As in the previous example we use the following parameters:\n",
     "\n",