Stop the ISO release when a step fails

omarchy-iso-release ran every step unconditionally: when docker denied
the build, it fell through to signing and uploading the newest stale
*-rc.iso from release/ under the new release's name — a six-month-old
ISO shipped as omarchy-4.0.2-rc.iso. set -e ends the release at the
first failed step, and also aborts when release/ holds no ISO for the
ref at all.

bin/omarchy-iso-release

@@ -1,5 +1,10 @@
 #!/bin/bash
 
+# A failed step must stop the release: without this, a make that dies (say,
+# docker permission denied) falls through to signing and uploading whatever
+# stale ISO release/ already holds, under the new release's name.
+set -e
+
 MAKE_ARGS=()
 ISO_REF=quattro
 RELEASE_SUFFIX=""