fix: fix scanner.c compile error

[elanora96]

After cloning the main branch, running make 4.4.1 with gcc 14.1.1 on Linux 6.9.6 in the lua/wincent/commandt/lib folder produced

❯ make
cc -Wall -Wextra -Wno-unused-parameter -DMAX_FILES_CONF=134217728 -DMMAP_SLAB_SIZE_CONF=137438953472 -DNDE
BUG -O3 -DLINUX -pthread -shared -fPIC -o commandt.so commandt.c debug.c die.c find.c heap.c matcher.c sca
nner.c score.c str.c watchman.c xmalloc.c xmap.c xstrdup.c
scanner.c: In function ‘commandt_scanner_new_command’:
scanner.c:160:9: error: implicit declaration of function ‘wait’ [-Wimplicit-function-declaration]
  160 |     if (wait(&child_pid) == -1) {
      |         ^~~~
make: *** [Makefile:62: commandt.so] Error 1

Including <sys/wait.h> in scanner.c for wait() allows for compilation

[wincent]

Thanks for this @elanora96! 🙇🏻