Use windows instead of ubuntu to meet .NET 4.6.1 requirements

Author: r-brown

.github/workflows/netlicensing-csharp-ci.yml

@@ -8,7 +8,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: windows-latest
     steps:
     - uses: actions/checkout@v2
     - name: Setup .NET Core

.github/workflows/netlicensing-csharp-release.yml

@@ -9,7 +9,7 @@ on:
 
 jobs:
   publish-nuget:
-    runs-on: ubuntu-latest
+    runs-on: windows-latest
     steps:
     - uses: actions/checkout@v2
     - name: Setup .NET Core