removed unnecessary suffix for exported solution name

[bambooch]

The managed solution is exported in the Export solution as managed step of the convert-to-managed job with the solution-output-file property set as ${{ inputs.solution_shipping_folder}}/${{ inputs.solution_name }}.zip. The step Import solution to prod env in the release-to-staging job then tries to reference this file with the solution-file property set to ${{ inputs.solution_release_folder}}/${{ inputs.solution_name }}_managed.zip but this file doesn't exist resulting in a failed workflow run. Removing the _managed suffix from the file name that is trying to be resolved solves this issue.