make depend fails with gcc: error: dnstap.pb-c.c: No such file or directory

On v9_11 make depend prints:

$ make depend >/dev/null
gcc: error: dnstap.pb-c.c: No such file or directory
dnstap-read.c:51:10: fatal error: dns/dnstap.pb-c.h: No such file or directory
   51 | #include <dns/dnstap.pb-c.h>
      |          ^~~~~~~~~~~~~~~~~~~
compilation terminated.

On v9_11 and v9_16 the command make depend | grep "error:" && exit 1 from .gitlab-ci.yml won't work because the these errors go to stderr and we look for then on stdin. make depend 2>&1 | grep "error:" && exit 1 should do.