tests: fix LDADD

Problem reported by Christian Weisgerber <naddy@mips.inka.de> in:
https://lists.gnu.org/r/bug-tar/2023-07/msg00015.html
* tests/Makefile.am (LDADD): Add $(LIBINTL), $(LIBICONV).

tests/Makefile.am

@@ -337,4 +337,5 @@ AM_CPPFLAGS = \
 LDADD = ../gnu/libgnu.a\
  $(LIB_ACL) $(LIB_CLOCK_GETTIME) $(LIB_EACCESS)\
  $(LIB_GETRANDOM) $(LIB_HARD_LOCALE) $(FILE_HAS_ACL_LIB) $(LIB_MBRTOWC)\
- $(LIB_SELINUX) $(LIB_SETLOCALE_NULL)
+ $(LIB_SELINUX) $(LIB_SETLOCALE_NULL) \
+ $(LIBINTL) $(LIBICONV)