Add incremental system test progress to job summary

[PranjalManhgaye]

Write progress entries to GITHUB_STEP_SUMMARY after each finished system test while keeping the final results table.

Description

Closes #791.

This PR adds incremental progress reporting to the system tests job summary, instead of only writing the summary table after the full suite completes, the runner now:

• initializes a System tests progress section in GITHUB_STEP_SUMMARY
• appends one markdown bullet after each finished system test
• keeps the final system test results table at the end
  Locally verified incremental GITHUB_STEP_SUMMARY updates (progress bullets after each test + final table).
  This makes long-running system test workflows easier to follow from the GitHub Actions summary page.

Validation

verified locally by writing to a temporary GITHUB_STEP_SUMMARY file and by running release_test locally to confirm that progress entries are appended during execution and that the final results table is still written.

Checklist

• I added a summary of any user-facing changes (compared to the last release) in the changelog-entries/<PRnumber>.md.
• New tutorial case (e.g., new fluid-openfoam folder for existing tutorial)? Add it to the respective README.md.
• New tutorial? Update the website.
  • Add a sidebar entry
  • Add it to the overview

Resources

• Contributing tutorials
• System tests documentation