Actions: dependency caching

chances are this probably won't do much, i'll revert this commit if this doesn't

.github/workflows/ci.yml

@@ -16,7 +16,14 @@ jobs:
 
     - uses: actions/setup-dotnet@v3
       with:
-        dotnet-version: '6.x'
+        dotnet-version: '6.0.x'
+
+    - uses: actions/cache@v3
+      with:
+        path: ~/.nuget/packages
+        key: ${{ runner.os }}-nuget-${{ hashFiles('**/packages.lock.json') }}
+        restore-keys: |
+          ${{ runner.os }}-nuget
 
     - name: Restore dependencies
       run: dotnet restore