Bump external/bpf_conformance from `b1b1c21` to `1ce2861` #150

Job	Run time
build_ubuntu (Debug, tests)	25m 58s
build_windows (Debug, tests)	35m 16s
build_windows (Debug, library)	3m 49s
build_windows (Release, tests)	9m 8s
build_ubuntu (Debug, library)	1m 4s
build_ubuntu (Release, tests)	5m 58s
build_windows (Release, library)	5m 14s
build_ubuntu (Release, library)	1m 18s
	1h 27m 45s

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