workflow cleanups (#10)

Reviewed-on: #10
Co-authored-by: vickydotbat <vickydotbat@tutamail.com>
Co-committed-by: vickydotbat <vickydotbat@tutamail.com>

.gitea/workflows/test-image.yml

@@ -1,11 +1,11 @@
-# Test-build the Crucible image on PRs and main. Proves `nix build .#image`
-# still works (daemonless, Nix-built OCI tarball) but does NOT publish —
-# release publishing happens in build-image.yml on v* tags.
+# Test-build the Crucible image on PRs. Proves `nix build .#image` still works
+# (daemonless, Nix-built OCI tarball) but does NOT publish — release publishing
+# happens in build-image.yml on v* tags. PR-only: with up-to-date-before-merge
+# protection, main == the tested PR head, so a throwaway post-merge rebuild that
+# publishes nothing is pure waste.
 name: test-image
 
 on:
-  push:
-    branches: [main]
   pull_request:
 
 jobs: