fix: outputting matrix

Author: andhreljaKern

pi/diff.sh

@@ -37,12 +37,6 @@ for parent_image_type in "${UPDATED_PARENT_TYPES[@]}"; do
     done
 done
 
-MATRIX=$(cat <<EOF
-{
-    "parent_image_type": [${PARENT_IMAGE_TYPES::-1}],
-    "include": [${INCLUDES::-1}]
-}
-EOF
-)
+MATRIX='{"parent_image_type": ['${PARENT_IMAGE_TYPES::-1}'],"include": ['${INCLUDES::-1}']}'
 echo $MATRIX | jq -c --indent 2 '.'
 echo "matrix='$MATRIX'" >> $GITHUB_OUTPUT