sd-hwdb: include sys/stat.h in hwdb-internal.h
Include this header to fix errors when including hwdb-internal.h:
../src/libsystemd/sd-hwdb/hwdb-internal.h:16:21: error: field ‘st’ has incomplete type
16 | struct stat st;
(cherry picked from commit 9745b51c73c78a63003b4cb6e0714829144d297c)