[docs] Older GTK-Doc does not support HB_DEPRECATED_FOR() at all

Fixes CI build failure.

docs/Makefile.am

@@ -29,7 +29,7 @@ SCANGOBJ_OPTIONS=
 # Extra options to supply to gtkdoc-scan.
 # e.g. SCAN_OPTIONS=--deprecated-guards="GTK_DISABLE_DEPRECATED"
 SCAN_OPTIONS=--rebuild-types --deprecated-guards="HB_DISABLE_DEPRECATED" \
-	--ignore-decorators='HB_EXTERN|HB_DEPRECATED|HB_DEPRECATED_FOR()'
+	--ignore-decorators='HB_EXTERN|HB_DEPRECATED'
 
 # Header files or dirs to ignore when scanning. Use base file/dir names
 # e.g. IGNORE_HFILES=gtkdebug.h gtkintl.h private_code

docs/meson.build

@@ -56,7 +56,7 @@ gnome.gtkdoc('harfbuzz',
             join_paths(meson.current_build_dir(), '..'),
            ],
   scan_args: ['--deprecated-guards=HB_DISABLE_DEPRECATED',
-              '--ignore-decorators=HB_EXTERN|HB_DEPRECATED|HB_DEPRECATED_FOR()',
+              '--ignore-decorators=HB_EXTERN|HB_DEPRECATED',
              ],
   mkdb_args: ['--source-suffixes=h,cc',
               '--xml-mode',