Bump src/libshared from ca2f25f to 15cb6f9 (#3965)

Bumps [src/libshared](https://github.com/GothenburgBitFactory/libshared) from `ca2f25f` to `15cb6f9`.
- [Commits](GothenburgBitFactory/libshared@ca2f25f...15cb6f9)

---
updated-dependencies:
- dependency-name: src/libshared
  dependency-version: 15cb6f90f25758612d79f788095a4c3a9c090b89
  dependency-type: direct:production
...

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