Improve CI workflow for Droplet test

[olethanh]

• Only calculate the IP once.
• Do not include the configuration inside the Debian package but modify it directly inside the droplet.

Self proofreading checklist

• [x] The new code clear, easy to read and well commented.
• [x] New code does not duplicate the functions of builtin or popular libraries.
• [N/A] An LLM was used to review the new code and look for simplifications.
• [N/A] New classes and functions contain docstrings explaining what they provide.
• [of course] All new code is covered by relevant tests.
• [x] Documentation has been updated regarding these changes.

[hoh]

Tests on droplets were cancelled, restarted them :wink:

[hoh]

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 62.19%. Comparing base (fefb30d) to head (01de28f). Report is 9 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #691 +/- ## ======================================= Coverage 62.19% 62.19% ======================================= Files 69 69 Lines 6074 6074 Branches 641 641 ======================================= Hits 3778 3778 Misses 2144 2144 Partials 152 152 ```

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