Set GDB version number to 16.3.

This commit changes gdb/version.in to 16.3.

gdb/version.in

diff --git a/gdb/version.in b/gdb/version.in
index aea9ec6..b0bc340 100644
--- a/gdb/version.in
+++ b/gdb/version.in
@@ -1 +1 @@
-16.2.90.DATE-git
+16.3