auto/config: Emit error message to stderr in _sanitize_passes.

debian/changelog

@@ -2,6 +2,7 @@ livecd-rootfs (2.765) UNRELEASED; urgency=medium
 
   * auto/config: preserve germinate-output directory when removing config to
     speed up local iteration.
+  * auto/config: Emit error message to stderr in _sanitize_passes.
 
  -- Michael Hudson-Doyle <michael.hudson@ubuntu.com>  Tue, 24 May 2022 12:42:10 +1200
 

live-build/auto/config

@@ -305,7 +305,7 @@ _sanitize_passes ()
 		# if root pass, no parent to find
 		[ -z "$parent" ] && continue
 		if [ $(echo "$passes"|grep -cE "^$parent\$") -ne 1 ]; then
-			echo "ERROR: '$parent' is required by '$pass' but is missing. Registered passes are:\n$passes"
+			echo "ERROR: '$parent' is required by '$pass' but is missing. Registered passes are:\n$passes" >&2
 			exit 1
 		fi
 	done