mapl: Fix pflogger dependency (cherry-picking #39683 from spack/develop) #961

Job	Run time
clingo-cffi	26m 52s
shell	9m 17s
macos (3.10)	35m 50s
rhel8-platform-python	30m 30s
ubuntu (ubuntu-latest, 3.10, clingo, false)	51m 16s
ubuntu (3.10, ubuntu-latest, original, false)	25m 49s
ubuntu (3.6, ubuntu-20.04, clingo, false)	20m 48s
	3h 20m 22s

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