AK3: support custom AVBv1 signing with magiskboot

NOTE: this currently appears to be broken in magiskboot, so continue to use boot_signer for now, but we're ready for when it works ;)

META-INF/com/google/android/updater-script

@@ -3,4 +3,4 @@
 # Dummy file; update-binary is a shell script (DO NOT CHANGE)
 #
 #
-# AK_BASE_VERSION=20230904
+# AK_BASE_VERSION=20230910