shellcheck_run_steps: Use alternate shellcheck if specified

We were previously ignoring the --shellcheck setting.

Signed-off-by: dann frazier <dann.frazier@chainguard.dev>

Author: dannf

pre_commit_hooks/shellcheck_run_steps.py

@@ -58,7 +58,7 @@ def do_shellcheck(
             shfile.write(step["runs"])
             shfile.close()
         subprocess.check_call(
-            ["/usr/bin/shellcheck"]
+            shellcheck
             + shellcheck_args
             + ["--shell=busybox", "--"]
             + [os.path.basename(f.name) for _, f in all_steps],