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GHC 9.6.1-alpha1 doesn't bump template-haskell version

GHC 9.6.1-alpha1 bundles template-haskell-2.19.0.0:

$ ghc-pkg-9.6.0.20230111 list | grep template-haskell
    template-haskell-2.19.0.0

But this is the exact same version that GHC 9.4.4 bundles!

$ ghc-pkg-9.4.4 list | grep template-haskell
    template-haskell-2.19.0.0

Despite the version numbers being the same, there have been breaking changes to the template-haskell library in GHC 9.6.1-alpha1. See this section of the template-haskell changelog. Unfortunately, due to the version numbers being the same, it is not possible to guard against these changes with MIN_VERSION_template_haskell(...) CPP. (You have to instead resort to __GLASGOW_HASKELL__ hacks.)

Please consider bumping the template-haskell version to 2.20.0.0 to rectify this. It would also be nice to include a "Bump template-haskell" task in the new release tracking template (such as the one found in #22562 (closed), which already has a similar "Base base" task) so that this is not forgotten in the future.

Edited by Ryan Scott
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