fix(ci): export SHORT_SHA before yq env() calls

yq env(SHORT_SHA) requires SHORT_SHA as an environment variable,
not just a shell variable. Without export, yq cannot read it.

Regression from 0d610f5 (GRO-311).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/ci.yml

@@ -314,7 +314,7 @@ jobs:
           if [ -z "$TAG" ]; then
             TAG="$(date -u +%Y.%m.%d)-${GITHUB_SHA::7}"
           fi
-          SHORT_SHA="${SHA::7}"
+          export SHORT_SHA="${SHA::7}"
           echo "Updating dev overlay image tags to: $TAG"
           echo "Updating migration/seed Job names with SHA: $SHORT_SHA"
           cd /tmp/infra