[bit.cast] change "behaviour" to "behavior" (cplusplus#7353)

Author: Andreas-Krug

source/utilities.tex

@@ -15152,7 +15152,7 @@
 \item
 Otherwise, if $b$ is indeterminate, the behavior is undefined.
 \item
-Otherwise, the behaviour is erroneous, and the result is as specified above.
+Otherwise, the behavior is erroneous, and the result is as specified above.
 \end{itemize}
 The result does not otherwise contain any indeterminate or erroneous values.