Use multiline GITHUB_OUTPUT for changed files

Replace the single-line echo that wrote CHANGED_FILES to $GITHUB_OUTPUT with a here-document (key<<EOF ... EOF) to correctly export multi-line file lists. This preserves newlines and spaces in the changed-files output so downstream workflow steps receive the full list.

Author: C-Achard

.github/workflows/format.yml

@@ -23,7 +23,12 @@ jobs:
         run: |
           git fetch origin ${{ github.base_ref }}
           CHANGED_FILES=$(git diff --name-only origin/${{ github.base_ref }}...HEAD)
-          echo "changed=$CHANGED_FILES" >> $GITHUB_OUTPUT
+
+          {
+            echo "changed<<EOF"
+            echo "$CHANGED_FILES"
+            echo "EOF"
+          } >> "$GITHUB_OUTPUT"
 
       - name: Show changed files
         run: |