Rename NUGET_USER secret to NUGET_USERNAME

Author: Tyrrrz

.github/workflows/main.yml

@@ -29,5 +29,5 @@ jobs:
       package-version: ${{ inputs.package-version || (github.ref_type == 'tag' && github.ref_name) || format('0.0.0-ci-{0}', github.sha) }}
     secrets:
       CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
-      NUGET_USER: ${{ secrets.NUGET_USER }}
+      NUGET_USERNAME: ${{ secrets.NUGET_USERNAME }}
       DISCORD_WEBHOOK: ${{ secrets.DISCORD_WEBHOOK }}