[ci] Persist the integration test ccache across runs (#17735)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

.github/workflows/ci.yml

@@ -371,6 +371,18 @@ jobs:
         run: |
           sudo apt-get update -qq
           sudo apt-get install -y --no-install-recommends ccache
+      - name: Restore ccache (restore-only)
+        # esphome stores the PlatformIO ccache under the machine-global cache
+        # dir (see _ccache_env() in esphome/platformio/toolchain.py). The
+        # bucket-name prefix prefers a same-bucket seed; the bare prefix falls
+        # back to any seed when the bucket layout differs from dev.
+        uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+        with:
+          path: ~/.cache/esphome/platformio-ccache
+          key: integration-ccache-${{ matrix.bucket.name }}-${{ github.sha }}
+          restore-keys: |
+            integration-ccache-${{ matrix.bucket.name }}-
+            integration-ccache-
       - name: Set up Python 3.13
         id: python
         uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7.0.0
@@ -419,6 +431,14 @@ jobs:
         # esphome stores the PlatformIO ccache under the machine-global cache
         # dir (see _ccache_env() in esphome/platformio/toolchain.py).
         run: CCACHE_DIR="$HOME/.cache/esphome/platformio-ccache" ccache -s
+      - name: Save ccache
+        # Pull request saves land in per-PR scopes nothing else can reuse;
+        # dev pushes seed the shared copy instead.
+        if: github.event_name != 'pull_request'
+        uses: actions/cache/save@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+        with:
+          path: ~/.cache/esphome/platformio-ccache
+          key: integration-ccache-${{ matrix.bucket.name }}-${{ github.sha }}
 
   cpp-unit-tests:
     name: Run C++ unit tests