Add nuget caching to build

.github/workflows/build.yml

@@ -22,6 +22,14 @@ jobs:
         with:
           dotnet-version: '6.0.x'
         
+      - name: Cache NuGet packages 
+        uses: actions/cache@v1
+        with:
+          path: ~/.nuget/packages
+          key: ${{ runner.os }}-nuget-${{ hashFiles('**/*.csproj') }}
+          restore-keys: |
+            ${{ runner.os }}-nuget-
+
       - name: Install dependencies
         run: dotnet restore