Bump external/bpf_conformance from `1ce2861` to `b544539` #151

Job	Run time
build_ubuntu (Debug, tests)	26m 47s
build_windows (Debug, tests)	36m 48s
build_ubuntu (Debug, library)	1m 6s
build_windows (Debug, library)	5m 6s
build_ubuntu (Release, tests)	5m 57s
build_windows (Release, tests)	10m 11s
build_ubuntu (Release, library)	1m 21s
build_windows (Release, library)	4m 26s
	1h 31m 42s

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