[gspell] build: replace use of deprecated macro

[Sébastien Wilmet <swilmet src gnome org>]

commit 2473b48687c2a122100fa651e938cc344023a10b
Author: Sébastien Wilmet <swilmet informatique-libre be>
Date:   Sat Jul 30 20:24:53 2022 +0200

    build: replace use of deprecated macro
    
    See:
    https://git.savannah.gnu.org/cgit/autoconf.git/commit/?id=a1acd8e66b7a4ca348401f890b4f04a6ca6b7d15

 configure.ac | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/configure.ac b/configure.ac
index a1e5060..cac457f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -55,7 +55,7 @@ glib_req=2.44
 gtk_req=3.20
 
 AC_CONFIG_SRCDIR([gspell/gspell-checker.c])
-AC_CONFIG_HEADER([config.h])
+AC_CONFIG_HEADERS([config.h])
 AC_CONFIG_MACRO_DIR([m4])
 
 # gnu strictness to generate the INSTALL file