Update GHC used for our Haskell software

When deploying, the following warning is printed:

trace: WARNING: 8.10.6 is out of date, consider using 8.10.7.

See log.

Usually no biggie, but I suspect this makes the whole build take much longer since probably only the latest versions are in the NixOS binary caches.

mentioned in commit 0ea7228e

mentioned in merge request !579 (merged)

mentioned in merge request !576 (merged)

From a deploy of PrivateStorageIo to production:

trace: WARNING: 8.10.6 is out of date, consider using 8.10.7.

Fives times - that's the number of storage servers - so my PR to the payment server seems to have worked to get rid of the old stuff, but the storage server still has some obsolete Haskell infra somewhere.

It's LeaseReport. That software is tiny.

mentioned in merge request !581 (merged)

Remaining TODOs:

• Fix CI and merge https://github.com/PrivateStorageio/PaymentServer/pull/146
• Return to 'main' branch on our Haskell software !582 (merged)