containers version used in GHC 9.0 is missing several important bug fixes

The ghc-9.0 branch currently uses containers-0.6.2.1, which has several important correctness issues that were fixed in v0.6.3.1: http://hackage.haskell.org/package/containers-0.6.3.1/changelog.

I suggest that GHC 9.0 include the latest containers-0.6.4.1 instead.

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