[arabic] Update to AMTRA revision 6

https://www.unicode.org/reports/tr53/tr53-6.html#Modifications

src/hb-ot-shape-complex-arabic.cc

@@ -635,6 +635,11 @@ modifier_combining_marks[] =
   0x06E3u, /* ARABIC SMALL LOW SEEN */
   0x06E7u, /* ARABIC SMALL HIGH YEH */
   0x06E8u, /* ARABIC SMALL HIGH NOON */
+  0x08CAu, /* ARABIC SMALL HIGH FARSI YEH */
+  0x08CBu, /* ARABIC SMALL HIGH YEH BARREE WITH TWO DOTS BELOW */
+  0x08CDu, /* ARABIC SMALL HIGH ZAH */
+  0x08CEu, /* ARABIC LARGE ROUND DOT ABOVE */
+  0x08CFu, /* ARABIC LARGE ROUND DOT BELOW */
   0x08D3u, /* ARABIC SMALL LOW WAW */
   0x08F3u, /* ARABIC SMALL HIGH WAW */
 };