Update git_changelog to know that there's a 9.6 branch.

Missed this in the main 10devel version stamping patch.

src/tools/git_changelog

@@ -57,7 +57,7 @@ require IPC::Open2;
 # (We could get this from "git branches", but not worth the trouble.)
 # NB: master must be first!
 my @BRANCHES = qw(master
-  REL9_5_STABLE
+  REL9_6_STABLE REL9_5_STABLE
   REL9_4_STABLE REL9_3_STABLE REL9_2_STABLE REL9_1_STABLE REL9_0_STABLE
   REL8_4_STABLE REL8_3_STABLE REL8_2_STABLE REL8_1_STABLE REL8_0_STABLE
   REL7_4_STABLE REL7_3_STABLE REL7_2_STABLE REL7_1_STABLE REL7_0_PATCHES