Fix Rubocop CI failure in ForemanInventoryUpload.base_folder path selection update

[Copilot]

The Rubocop / Rubocop GitHub Actions job failed due to style violations introduced in the base_folder writable/fallback path update. This PR keeps the intended runtime behavior and aligns the implementation with repository Rubocop rules.

• CI failure source

  • Resolves Rubocop offenses in the updated ForemanInventoryUpload.base_folder logic (Layout/*Alignment, Layout/IndentationWidth, Rails/FilePath).

• Production code adjustments

  • Keeps shared tmpdir behavior: use /var/run/foreman when writable.
  • Keeps fallback behavior: use Rails.root/tmp/red_hat_inventory when shared tmpdir is unavailable/unwritable.
  • Refactors path construction/alignment to conform to repository cops.

• Focused test coverage

  • Adds/updates unit tests to explicitly cover:
    • writable shared tmpdir path selection
    • fallback Rails tmp path selection

base_path = if File.writable?(SHARED_TMPDIR)
              Pathname.new(SHARED_TMPDIR).join('red_hat_inventory')
            else
              Rails.root.join('tmp/red_hat_inventory')
            end
"#{base_path}/"