Update NuGet token in external workflow

Author: gwaldron

.github/workflows/external.yml

@@ -52,9 +52,9 @@ jobs:
           -StorePasswordInClearText `
           -Name GitHubPackages `
           -UserName "gwaldron" `
-          -Password "${{ secrets.GITHUB_TOKEN }}"
+          -Password "${{ secrets.NUGET_CACHE_TOKEN }}"
         .$(${{ matrix.VCPKG_WORKSPACE }}/vcpkg/vcpkg fetch nuget) `
-          setapikey "${{ secrets.GITHUB_TOKEN }}" `
+          setapikey "${{ secrets.NUGET_CACHE_TOKEN }}" `
           -Source "${{ env.FEED_URL }}"
 
     - name: Create Build Environment