Bump external/bpf_conformance from `ff36a50` to `318cc3b` #1538

Job	Run time
build_windows (Debug, tests)	41m 17s
build_windows (Debug, library)	3m 33s
build_ubuntu (Debug, tests)	20m 59s
build_windows (Release, tests)	10m 55s
build_windows (Release, library)	3m 56s
build_ubuntu (Debug, library)	1m 6s
build_ubuntu (Release, tests)	6m 1s
build_ubuntu (Release, library)	1m 15s
	1h 29m 2s

Provide feedback