fix: consistent equations between code and rendered version

Fixes quarto-dev/quarto-cli#11336

Author: mcanouil

docs/authoring/cross-references.qmd

@@ -366,7 +366,7 @@ Black-Scholes (@eq-black-scholes) is a mathematical model that seeks to explain
 
 $$
 \frac{\partial \mathrm C}{ \partial \mathrm t } + \frac{1}{2}\sigma^{2} \mathrm S^{2}
-\frac{\partial^{2} \mathrm C}{\partial \mathrm C^2}
+\frac{\partial^{2} \mathrm C}{\partial \mathrm S^2}
   + \mathrm r \mathrm S \frac{\partial \mathrm C}{\partial \mathrm S}\ =
   \mathrm r \mathrm C 
 $$ {#eq-black-scholes}
@@ -401,5 +401,3 @@ title: "My Document"
 number-sections: true
 ---
 ```
-
-