Bump external/libbtf from 2de28d7 to 2f68368

Bumps [external/libbtf](https://github.com/Alan-Jowett/libbtf) from `2de28d7` to `2f68368`.
- [Release notes](https://github.com/Alan-Jowett/libbtf/releases)
- [Commits](Alan-Jowett/libbtf@2de28d7...2f68368)

---
updated-dependencies:
- dependency-name: external/libbtf
  dependency-type: direct:production
...

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