🧪 [testing improvement] Add coverage for config_bashrc_d in github-tokens

[MiguelRodo]

🎯 What: Added missing test coverage for the config_bashrc_d function in the github-tokens feature to verify its behavior and idempotency.
📊 Coverage: The new test script (test/_global/github-tokens-bashrc-d.sh) covers three key scenarios:

1. When .bashrc does not exist (new environment).
2. When the script is run multiple times (idempotency, ensuring it doesn't duplicate the sourcing logic).
3. When .bashrc already exists with prior content.
   ✨ Result: Increased reliability of the dotfiles configuration by ensuring the bashrc.d setup logic works exactly as intended across various state conditions without destructive side effects.

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PR created automatically by Jules for task 15016881542144948095 started by @MiguelRodo

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