CI: Cache build trees, update some action versions

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
         with:
           path: pdf4qt
 
@@ -21,14 +21,15 @@ jobs:
           ./vcpkg integrate install
         
       - name: 'VCPKG: Cache vcpkg dependencies'
-        uses: actions/cache@v2
+        uses: actions/cache@v3
         with:
           path: |
+            ./vcpkg/buildtrees
             ./vcpkg/downloads
             ./vcpkg/packages
-          key: ${{ runner.os }}-vcpkg-${{ hashFiles('**/vcpkg.json') }}
+          key: ${{ runner.os }}-vcpkg-v2-${{ hashFiles('**/vcpkg.json') }}
           restore-keys: |
-            ${{ runner.os }}-vcpkg-
+            ${{ runner.os }}-vcpkg-v2-
 
       - name: 'VCPKG: Install project dependencies'
         run: |