Bump extern/fabm from f7057c4 to cebd56f

Bumps [extern/fabm](https://github.com/fabm-model/fabm-plus) from `f7057c4` to `cebd56f`.
- [Commits](fabm-model/fabm-plus@f7057c4...cebd56f)

---
updated-dependencies:
- dependency-name: extern/fabm
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>