Fixed typo

Author: sponce

talk/expert/cpp20concepts.tex

@@ -150,7 +150,7 @@
         \item a concept can be used together with \mintinline{cpp}{auto} to impose requirements on the type of a variable
       \end{itemize}
     \end{block}
-    \begin{exampleblock}{firstnumber=4,gobble=2}
+    \begin{exampleblock}{Example code}
       \begin{cppcode*}{firstnumber=4,gobble=2}
       MyFloatingPoint auto f = 3.14f;
       MyFloatingPoint auto d = 3.14;