Bump idna from 3.7 to 3.15 in /xkcd_download (#559)

Bumps [idna](https://github.com/kjd/idna) from 3.7 to 3.15.
- [Release notes](https://github.com/kjd/idna/releases)
- [Changelog](https://github.com/kjd/idna/blob/master/HISTORY.md)
- [Commits](kjd/idna@v3.7...v3.15)

---
updated-dependencies:
- dependency-name: idna
  dependency-version: '3.15'
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

xkcd_download/requirements.txt

@@ -1,7 +1,7 @@
 beautifulsoup4==4.9.3
 certifi==2024.7.4
 chardet==3.0.4
-idna==3.7
+idna==3.15
 lxml==6.1.0
 requests==2.33.0
 soupsieve==2.0.1