ci: fix ccache dir path — runner.temp is not a valid expression context

Point CCACHE_DIR and the cache action at a fixed workspace directory
instead; checkout cleans untracked files before the restore, so the
ordering is safe.

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
         os: [warp-ubuntu-latest-x64-8x, warp-macos-15-arm64-12x, warp-windows-latest-x64-8x]
     env:
       CMAKE_BUILD_TYPE: Release
-      CCACHE_DIR: ${{ runner.temp }}/ccache
+      CCACHE_DIR: ${{ github.workspace }}/.ccache
       CCACHE_MAXSIZE: 1G
       # Enable OFX integration tests that require external plugin bundles
       RUN_OFX_ITEST: "1"
@@ -110,7 +110,7 @@ jobs:
       - name: Restore ccache
         uses: WarpBuilds/cache@v1
         with:
-          path: ${{ runner.temp }}/ccache
+          path: ${{ github.workspace }}/.ccache
           key: ccache-${{ runner.os }}-${{ github.ref_name }}-${{ github.sha }}
           restore-keys: |
             ccache-${{ runner.os }}-${{ github.ref_name }}-
@@ -276,7 +276,7 @@ jobs:
     env:
       CMAKE_BUILD_TYPE: Release
       QT_QPA_PLATFORM: offscreen
-      CCACHE_DIR: ${{ runner.temp }}/ccache
+      CCACHE_DIR: ${{ github.workspace }}/.ccache
       CCACHE_MAXSIZE: 1G
 
     steps:
@@ -297,7 +297,7 @@ jobs:
       - name: Restore ccache
         uses: WarpBuilds/cache@v1
         with:
-          path: ${{ runner.temp }}/ccache
+          path: ${{ github.workspace }}/.ccache
           key: ccache-${{ runner.os }}-dynamic-${{ github.ref_name }}-${{ github.sha }}
           restore-keys: |
             ccache-${{ runner.os }}-dynamic-${{ github.ref_name }}-