Add compat entry for Base.donotdelete (#55773)

(cherry picked from commit 346f38b)

Author: LilithHafner

base/docs/basedocs.jl

@@ -3293,6 +3293,9 @@ unused and delete the entire benchmark code).
     `donotdelete(1+1)`, no add instruction needs to be executed at runtime and
     the code is semantically equivalent to `donotdelete(2).`
 
+!!! compat "Julia 1.8"
+    This method was added in Julia 1.8.
+
 # Examples
 
 ```julia