Fix #6531 Use GitHub-hosted Ubuntu/AArch64 runner

From 2025-01-16, GitHub has provided Linux/AArch64 runners (in public preview), see:

https://github.blog/changelog/2025-01-16-linux-arm64-hosted-runners-now-available-for-free-in-public-repositories-public-preview/

Previously, the Stack project used a self-hosted runner for Linux/AArch64, using a machine donated by FP Complete.

This commit:

* removes the `configuration` job, that checked for self-hosted runners;

* removes the `linux-arm64` job, which used `release.hs build --alpine --stack-args --docker-stack-exe=image`;

* moves the functionality of the old `linux-arm64` job to the `integration-tests` job, making use of the `ubuntu-24.04-arm` GitHub-hosted runner;

* as that runner does not come with Haskell tools, installs the current version of Stack; and

* updates some of the comments in the workflow, accordingly.

As previously, it seems unnecessary to run integration tests for Linux/AArch64, given that they are run for Linux/x86_64.

Stack's online documentation will be updated separately, as it targets a different branch (`stable`).

Fix #6675 Add install-msys and ancillary matters

Fix #6678 Add Cabal boot package to `setup-depends` deps, when needed

Has the side-effect of bumping cabal-version to 2.2.

Dev Containers: Add 'GHC 9.12.1'

Re #6670 Extend S-8432 for non-Latin1 in Stack 'programs' path