Cache CPM on CI.

.github/workflows/linux.yml

@@ -20,6 +20,12 @@ jobs:
     - name: Trust git repo
       run: git config --global --add safe.directory '*'
     - uses: actions/checkout@v4
+    - name: Cache CPM packages
+      uses: actions/cache@v4
+      with:
+        path: ${{ env.CPM_SOURCE_CACHE }}
+        key: ${{ runner.os }}-cpm-${{ hashFiles('**/vendor.cmake', '**/CMakeLists.txt') }}
+        restore-keys: ${{ runner.os }}-cpm-
     - name: Profiler GUI
       run: |
         cmake -B profiler/build -S profiler -DCMAKE_BUILD_TYPE=Release -DGIT_REV=${{ github.sha }}