Fix AIX CI build break.

In AIX a recent commit caused a build break with the error as shown below.
In file included from python/py-color.h:23,
                 from python/python.c:39:
python/python-internal.h:86:10: fatal error: Python.h: No such file or directory
   86 | #include <Python.h>

In AIX, we run builds with and without python for our internal CI's.

A feature development made by the recent commit https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=6447969d0ac774b6dec0f95a0d3d27c27d158690
missed to guard Python.h in HAVE_PYTHON macro.

This commit is a fix for the same.

Approved-By: Tom Tromey <tom@tromey.com>

gdb/python/python.c

@@ -36,7 +36,6 @@
 #include "run-on-main-thread.h"
 #include "observable.h"
 #include "build-id.h"
-#include "py-color.h"
 
 #if GDB_SELF_TEST
 #include "gdbsupport/selftest.h"
@@ -78,6 +77,7 @@ static const char *gdbpy_should_print_stack = python_excp_message;
 #include "interps.h"
 #include "event-top.h"
 #include "py-event.h"
+#include "py-color.h"
 
 /* True if Python has been successfully initialized, false
    otherwise.  */