update publish workflow to publish to official nuget as well

Author: popcron

.github/workflows/publish.yml

@@ -104,10 +104,15 @@ jobs:
       - name: Pack `Physics.Systems`
         run: dotnet pack "${{ github.event.repository.name }}/source" /p:Version=${VERSION} --no-build --output .
 
-      - name: Add NuGet Source
+      - name: Add GitHub source
         run: dotnet nuget add source https://nuget.pkg.github.com/${{ github.repository_owner }}/index.json --name github --username ${{ github.repository_owner }} --password ${{ github.token }} --store-password-in-clear-text
 
-      - name: Publish `Physics.Systems`
-        run: dotnet nuget push SimulationTree.Physics.Systems.${VERSION}.nupkg --source github --api-key ${NUGET_TOKEN}
+      - name: Publish `Physics.Systems` to GitHub registry
+        run: dotnet nuget push SimulationTree.Physics.Systems.${VERSION}.nupkg --source github --api-key ${API_KEY}
         env:
-          NUGET_TOKEN: ${{ secrets.NUGET_TOKEN }}
+          API_KEY: ${{ secrets.NUGET_TOKEN_GITHUB }}
+      
+      - name: Publish `Physics.Systems` to official registry
+        run: dotnet nuget push SimulationTree.Physics.Systems.${VERSION}.nupkg --source nuget.org --api-key ${API_KEY}
+        env:
+          API_KEY: ${{ secrets.NUGET_TOKEN_OFFICIAL }}