update github action to v3

.github/workflows/ci.yml

@@ -45,7 +45,7 @@ jobs:
     runs-on: ${{ matrix.builder }}
     steps:
       - name: Checkout nim-zlib
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           submodules: true
 
@@ -93,7 +93,7 @@ jobs:
       - name: Restore Nim DLLs dependencies (Windows) from cache
         if: runner.os == 'Windows'
         id: windows-dlls-cache
-        uses: actions/cache@v2
+        uses: actions/cache@v3
         with:
           path: external/dlls
           key: 'dlls'