Fix typo

Correct "ctions" to "actions".

concurrency-primer.tex

@@ -855,7 +855,7 @@ \subsection{Acquire and release}
 We have just examined the acquire and release operations in the context of the lock example from \secref{lock-example}.
 You can think of them as ``one-way'' barriers: an acquire operation permits other reads and writes to move past it,
 but only in a $before \to after$ direction.
-A release works the opposite manner, allowing ctions to move in an $after \to before$ direction.
+A release works the opposite manner, allowing actions to move in an $after \to before$ direction.
 On \textsc{Arm} and other weakly-ordered architectures, this enables us to eliminate one of the memory barriers in each operation,
 such that