Add a NEWS entry for find* and indexin sentinel change

[ci skip]

Author: ararslan

NEWS.md

@@ -397,6 +397,10 @@ This section lists changes that do not have deprecation warnings.
     and higher-dimensional arrays insted of linear indices as was previously the case.
     Use `LinearIndices(a)[findall(f, a)]` and similar constructs to compute linear indices.
 
+  * The `find*` functions which return scalars, i.e. `findnext`, `findprev`, `findfirst`,
+    and `findlast`, as well as `indexin`, now return `nothing` when no match is found rather
+    than 0 ([#25472], [#25662]).
+
   * The `Base.HasShape` iterator trait has gained a type parameter `N` indicating the
     number of dimensions, which must correspond to the length of the tuple returned by
     `size` ([#25655]).