Update changelog for scandump version 2.1.5

[adriangranados]

Fixes issues with frequency argument parsing and prevents infinite loops on errors.

Type of change

• Bug fix (non-breaking change that fixes something)
• Documentation update (readme, changelog, man page, etc.)
• New feature (non-breaking change adding functionality)
• Breaking change (fix or feature changing existing functionality)
• Code quality improvement (refactor, performance improvements)
• Other (please specify):

Breaking change

• What functionality breaks?
• Why does it break?
• How should it be migrated?
• Are there any backward-compatible alternatives?

Proposed change

Replace this line with what your change is about. Why, what, and implementations details are helpful.

Testing

• Did you add new automated tests? If yes, explain which edge cases are covered.
• Does this change affect any existing tests? If so, how did you adjust them?
• Please provide test run results or screenshots if applicable.

LLM/AI usage

• I used an LLM or AI coding assistant for this PR
• If yes, please describe:
  • Which tool(s) and model(s) were used (e.g., Gemini 2.5 Flash, Claude 4.5 Sonnet, Copilot GPT-4, ChatGPT GPT-5)?
  • What portions of the code and PR were assisted?
  • Have you reviewed and tested all generated code for correctness?

Checklist

• I have read the contribution guidelines and policies
• I have targeted this PR against the correct git branch (this can vary depending on the default branch of the repo)
• I ran the test suite and verified it succeeded
• I linked a GitHub issue to this PR (in the next section).
• I have updated the changelog (if applicable)
• I have added or updated the documentation (if applicable)

Related Issues/PRs

• This PR fixes/closes issue #
• This PR is related to issue #
• This PR depends on/blocks PR #