format_check: properly export changed files

When multiple files change, tj-action/changed-files separates file names
with a space, so the output is ambiguous. Switch to JSON output and use
jq to convert the array to a text file with one file name per line, a
format that is readily usable for clang-format-action.

Signed-off-by: Luca Burelli <[email protected]>

Author: pillo79

.github/workflows/format_check.yml

@@ -37,13 +37,15 @@ jobs:
             libraries/examples/**
             libraries/extras/**
             libraries/ea_malloc/**
-          write_output_files: true
-      - name: List changed files
+          json: true
+      - name: Export changed files in a text file, one per line
         if: steps.changed-files.outputs.any_changed == 'true'
-        run: cat .github/outputs/all_changed_files.txt
+        run: |
+          echo ${{ steps.changed-files.outputs.all_changed_files }} | jq -r '.[]' > all_changed_files.txt
+          cat all_changed_files.txt
       - name: Run clang-format check
         if: steps.changed-files.outputs.any_changed == 'true'
         uses: pillo79/clang-format-action@05f671e71f0758aba4d3c9dbb0ee81bc5f0137c6
         with:
           clang-format-version: '19'
-          check-files-from: .github/outputs/all_changed_files.txt
+          check-files-from: all_changed_files.txt