Use setup-nuget to fix broken nuget in GitHub actions

All Windows builds were failing to download clcache from nuget. This
problem also documented in
actions/runner-images#3240. Follow
their approach to fix the nuget setup.

Author: tautschnig

.github/workflows/pull-request-checks.yaml

@@ -300,6 +300,9 @@ jobs:
       - uses: actions/checkout@v2
         with:
           submodules: recursive
+      - uses: nuget/setup-nuget@v1
+        with:
+          nuget-version: 'latest'
       - name: Fetch dependencies
         run: |
           choco install winflexbison3 strawberryperl
@@ -400,6 +403,9 @@ jobs:
       - uses: actions/checkout@v2
         with:
           submodules: recursive
+      - uses: nuget/setup-nuget@v1
+        with:
+          nuget-version: 'latest'
       - name: Fetch dependencies
         run: |
           choco install winflexbison3

.github/workflows/release-packages.yaml

@@ -148,6 +148,9 @@ jobs:
       - uses: actions/checkout@v2
         with:
           submodules: recursive
+      - uses: nuget/setup-nuget@v1
+        with:
+          nuget-version: 'latest'
       - name: Fetch dependencies
         run: |
           choco install winflexbison3