run: include sys/stat.h again

This partially reverts 9adb4685df.

For the case that sys/stat.h is not included indirectly by other headers.
Fixes the following error:
```
../src/run/run.c: In function 'fchown_to_capsule':
../src/run/run.c:2128:21: error: storage size of 'st' isn't known
 2128 |         struct stat st;
      |                     ^~
```

src/run/run.c

@@ -5,6 +5,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/resource.h>
+#include <sys/stat.h>
 #include <unistd.h>
 
 #include "sd-bus.h"