tree-wide: sort includes

Sort the includes accoding to the new coding style.

src/test/test-utf8.c

@@ -20,9 +20,9 @@
 ***/
 
 #include "alloc-util.h"
+#include "string-util.h"
 #include "utf8.h"
 #include "util.h"
-#include "string-util.h"
 
 static void test_utf8_is_printable(void) {
         assert_se(utf8_is_printable("ascii is valid\tunicode", 22));