ci: update lock file on dependabot pushed (#29)

workaround for dependabot/dependabot-core#1303

.github/workflows/dependabot-restore.yml

@@ -0,0 +1,46 @@
+name: Update NuGet Lock file
+
+on:
+  push:
+    branches:
+      - dependabot/nuget/**
+
+jobs:
+  update:
+    name: Update NuGet Lock file
+    if: contains(github.actor, 'dependabot')
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2.3.4
+      - uses: actions/cache@v2.1.6
+        with:
+          path: ${{ env.NUGET_PACKAGES }}
+          key: ${{ runner.os }}-nuget-${{ hashFiles('**/packages.lock.json') }}
+          restore-keys: |
+            ${{ runner.os }}-nuget-
+
+      - name: Setup .NET Core 3.1 SDK
+        uses: actions/setup-dotnet@v1.8.1
+        with:
+          dotnet-version: 3.1.x
+      - name: Setup .NET 5.0 SDK
+        uses: actions/setup-dotnet@v1.8.1
+        with:
+          dotnet-version: 5.0.x
+
+      - name: Restore
+        run: dotnet restore
+
+      - name: Count changes
+        id: changes
+        run: |
+          git add -N .
+          echo "::set-output name=count::$(git diff --name-only | wc -l)"
+      - name: Commit & Push
+        if: steps.changes.outputs.count > 0
+        run: |
+          git config user.name github-actions
+          git config user.email github-actions@github.com
+          git add .
+          git commit -m "chore(deps): update NuGet lock files"
+          git push