Bump magic numbers for 5.2.0minus-7 (#3627)

Author: ccasin

build-aux/ocaml_version.m4

@@ -97,7 +97,7 @@ m4_define([OCAML__RELEASE_EXTRA],
 # - A 3-bytes version number
 
 m4_define([MAGIC_NUMBER__PREFIX], [Caml1999])
-m4_define([MAGIC_NUMBER__VERSION], [556])
+m4_define([MAGIC_NUMBER__VERSION], [557])
 
 # The following macro is used to define all our magic numbers
 # Its first argument is the name of the file type described by that