chore(ci): fix error in clang-tidy-differential with diffs in multiple files (#7685)

* chore(ci): output modified file list without newlines

Signed-off-by: Kotaro Yoshimoto <pythagora.yoshimoto@gmail.com>

* chore(ci): test diffs

Signed-off-by: Kotaro Yoshimoto <pythagora.yoshimoto@gmail.com>

* chore(ci): test diffs

Signed-off-by: Kotaro Yoshimoto <pythagora.yoshimoto@gmail.com>

* chore(ci): revert test diff

Signed-off-by: Kotaro Yoshimoto <pythagora.yoshimoto@gmail.com>

* chore(ci): revert test diff

Signed-off-by: Kotaro Yoshimoto <pythagora.yoshimoto@gmail.com>

---------

Signed-off-by: Kotaro Yoshimoto <pythagora.yoshimoto@gmail.com>

Author: HansRobo

.github/workflows/clang-tidy-differential.yaml

@@ -38,7 +38,7 @@ jobs:
       - name: Get modified files
         id: get-modified-files
         run: |
-          echo "changed_files=$(git diff --name-only "origin/${{ github.base_ref }}"...HEAD | grep -E '\.(cpp|hpp)$' || true)" >> $GITHUB_OUTPUT
+          echo "changed_files=$(git diff --name-only "origin/${{ github.base_ref }}"...HEAD | grep -E '\.(cpp|hpp)$' | tr '\n' ' ' || true)" >> $GITHUB_OUTPUT
         shell: bash
 
       - name: Run clang-tidy