code quote the atomic orderings in the manual (#41902)

Author: KristofferC

doc/src/manual/multi-threading.md

@@ -244,8 +244,8 @@ which will later be published formally.
 
 Any field in a struct declaration can be decorated with `@atomic`, and then any
 write must be marked with `@atomic` also, and must use one of the defined atomic
-orderings (:monotonic, :acquire, :release, :acquire\_release, or
-:sequentially\_consistent). Any read of an atomic field can also be annotated
+orderings (`:monotonic`, `:acquire`, `:release`, `:acquire_release`, or
+`:sequentially_consistent`). Any read of an atomic field can also be annotated
 with an atomic ordering constraint, or will be done with monotonic (relaxed)
 ordering if unspecified.