Exclude buggy Toil 5.6

Marcel Looserequested to merge
RAP-500-exclude-Toil5.6 into master

Exclude Toil version 5.6, because it contains a nasty file renaming bug, that is (sometimes) triggered in scatter jobs operating on Measurement Sets. See https://github.com/DataBiosphere/toil/issues/4101 for details.

Closes RAP-500

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