fix: deprecate firewall_already_removed error code

[jooola]

Related to https://docs.hetzner.cloud/changelog#2025-08-04-multiple-api-behavior-changes-for-firewalls

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.27%. Comparing base (2d79664) to head (2c7f851).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #748   +/-   ##
=======================================
  Coverage   78.27%   78.27%           
=======================================
  Files          55       55           
  Lines        5023     5023           
=======================================
  Hits         3932     3932           
  Misses        824      824           
  Partials      267      267           

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