core: Add two more IWYU pragmas

If selinux isn't enabled, these are reported as unused, so let's
add pragmas to tell clang-tidy to keep these.

src/core/dbus.c

@@ -39,7 +39,7 @@
 #include "path-util.h"
 #include "pidref.h"
 #include "process-util.h"
-#include "selinux-access.h"
+#include "selinux-access.h"     /* IWYU pragma: keep */
 #include "serialize.h"
 #include "set.h"
 #include "special.h"

src/core/load-fragment.c

@@ -57,7 +57,7 @@
 #include "reboot-util.h"
 #include "seccomp-util.h"
 #include "securebits-util.h"
-#include "selinux-util.h"
+#include "selinux-util.h"               /* IWYU pragma: keep */
 #include "set.h"
 #include "show-status.h"
 #include "signal-util.h"