Bump external/libbtf from ab8d59b to aa0e588

Bumps [external/libbtf](https://github.com/Alan-Jowett/libbtf) from `ab8d59b` to `aa0e588`.
- [Release notes](https://github.com/Alan-Jowett/libbtf/releases)
- [Commits](Alan-Jowett/libbtf@ab8d59b...aa0e588)

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

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