Bump external/bpf_conformance from `1ce2861` to `b544539` #1440

Job	Run time
build_ubuntu (Debug, tests)	26m 56s
build_windows (Debug, tests)	36m 47s
build_ubuntu (Debug, library)	1m 18s
build_windows (Debug, library)	4m 32s
build_ubuntu (Release, tests)	5m 57s
build_windows (Release, tests)	9m 58s
build_ubuntu (Release, library)	1m 8s
build_windows (Release, library)	5m 7s
	1h 31m 43s

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