Bumping megaparsec, tasty #317

Job	Run time
docs (8.10)	4m 52s
Enumerate CI configurations	7s
build (ghc-8.10.7)	5m 13s
build (ghc-9.0.2)	7m 19s
build (ghc-9.2.4)	6m 38s
build (ghc-9.2.5)	5m 4s
build (ghc-9.4.4)	6m 15s
build (ghc-9.6.1)	5m 30s
build (stackage-20.5)	5m 15s
build (stackage-21.6)	6m 5s
build (stackage-nightly)	5m 12s
build (upper-bounds)	2m 50s
Calculate cabal bounds	11s
	1h 0m 31s

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