docs: make encryption example in line with docs

[Ernst79]

The docs did not match with the encryption example. This PR fixes this.

This fix should be merged together with this PR for the docs.
home-assistant/bthome.io#69

Fix #324

[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.11%. Comparing base (1c8d3a1) to head (219bce9).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/bthome_ble/bthome_v2_encryption.py	25.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #334      +/-   ##
==========================================
- Coverage   83.21%   83.11%   -0.10%     
==========================================
  Files           6        6              
  Lines         685      687       +2     
  Branches      101      101              
==========================================
+ Hits          570      571       +1     
- Misses         88       89       +1     
  Partials       27       27              

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