Bump external/bpf_conformance from 514fa97 to 28ddd7f

Bumps [external/bpf_conformance](https://github.com/Alan-Jowett/bpf_conformance) from `514fa97` to `28ddd7f`.
- [Release notes](https://github.com/Alan-Jowett/bpf_conformance/releases)
- [Commits](Alan-Jowett/bpf_conformance@514fa97...28ddd7f)

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

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