flydra_core,flydra_analysis: fix build errors #236

Job	Run time
test-ubuntu-system-python (ubuntu-20.04)	1m 16s
build (ubuntu-20.04, 3.8)	13s
test-ubuntu-system-python (ubuntu-latest)	1m 32s
build (ubuntu-20.04, 3.x)	2m 25s
build (ubuntu-latest, 3.8)	12s
build (ubuntu-latest, 3.x)	2m 20s
build (macos-11, 3.8)	1s
build (macos-11, 3.x)	1s
build (macos-latest, 3.8)	1m 18s
build (macos-latest, 3.x)	2m 17s
build (windows-2019, 3.8)	42s
build (windows-2019, 3.x)	5m 14s
build (windows-latest, 3.8)	53s
build (windows-latest, 3.x)	5m 1s
	23m 25s

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