(beginning-of-defun-raw): Suppress warning about syntax-begin-function

* lisp/emacs-lisp/lisp.el (beginning-of-defun-raw):
font-lock-compile-keywords also suppresses warnings about the
obsolete syntax-begin-function variable, so suppress the only
other use not in syntax.el.
1 job for master in 9 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
failed #2125
test-all

00:00:09

 
Name Stage Failure
failed
test-all Test There has been a runner system failure, please try again
Running with gitlab-runner 11.6.0 (f100a208)
on gitlab-runner-docker cff9d373
Using Docker executor with image debian:stretch ...
Pulling docker image debian:stretch ...
Using docker image sha256:e1de74e67cc70422153600785c4ce4c29843a0e59e18b634c52ca133c564437f for debian:stretch ...
ERROR: Job failed (system failure): Error response from daemon: failed to start shim: exec: "docker-containerd-shim": executable file not found in $PATH: unknown (executor_docker.go:1018:3s)