Fix sanitizer builds with clang (#1402)

By including <stdatomic.h> after the other includes in the unit test, we
can avoid redefining a macro which led to a build failure.

Fixes #1394

---------

Signed-off-by: Viktor Söderqvist <viktor.soderqvist@est.tech>

src/unit/test_networking.c

@@ -1,9 +1,9 @@
-#include <stdatomic.h>
-
 #include "../networking.c"
 #include "../server.c"
 #include "test_help.h"
 
+#include <stdatomic.h>
+
 int test_backupAndUpdateClientArgv(int argc, char **argv, int flags) {
     UNUSED(argc);
     UNUSED(argv);