ci: Set CCACHE_DIR explicitly

Author: kou

.github/workflows/test.yaml

@@ -92,10 +92,13 @@ jobs:
             libgirepository1.0-dev \
             libxsimd-dev \
             meson
+      - name: Prepare ccache
+        run: |
+          echo "CCACHE_DIR=${PWD}/.ccache" >> "${GITHUB_ENV}"
       - name: Cache ccache
         uses: actions/cache@v5
         with:
-          path: .cache/ccache/
+          path: ${{ env.CCACHE_DIR }}
           key: ccache-apache-arrow-${{ hashFiles('apache-arrow/cpp/**', 'apache-arrow/c_glib/**', 'apache-arrow/ruby/red-arrow/ext/**') }}
           restore-keys: ccache-apache-arrow-
       - name: Install Red FlatBuffers