Use default bakery version for PR builds

The head_ref pattern used by other CI jobs breaks on fork
PRs because the fork's branch doesn't exist in the base
repo. The PR build job uses the default "main" version
instead, which always resolves.

Author: bschwedler

.github/workflows/ci.yml

@@ -137,7 +137,9 @@ jobs:
 
     uses: "./.github/workflows/bakery-build-pr.yml"
     with:
-      version: ${{ github.head_ref || github.ref_name }}
+      # Don't pass version — default "main" is correct here. The head_ref
+      # pattern used by other jobs breaks on fork PRs because the fork's
+      # branch doesn't exist in posit-dev/images-shared.
       context: "./posit-bakery/test/resources/multiplatform/"
       dev-versions: include