Upgrade to heroku-24 stack

[paulcretu]

Upgrading to heroku-24 stack

Git is no longer available at runtime:

We made some tools that are typically only required during the build (such as GCC, Make, Git and system Python) available only at build time, rather than at app run time too.

This seems to cause problems with some mix tasks (e.g. when running mix ecto.migrate during release phase:

** (ErlangError) Erlang error: :enoent
    (elixir 1.15.6) lib/system.ex:1092: System.cmd("git", ["--git-dir=.git", "config", "remote.origin.url"], [cd: "/app/deps/zappa"])
    (mix 1.15.6) lib/mix/scm/git.ex:265: Mix.SCM.Git.get_rev_info/0
    (mix 1.15.6) lib/mix/scm/git.ex:75: anonymous fn/2 in Mix.SCM.Git.lock_status/1
    (elixir 1.15.6) lib/file.ex:1624: File.cd!/2
    (mix 1.15.6) lib/mix/dep.ex:432: Mix.Dep.check_lock/1
    (elixir 1.15.6) lib/enum.ex:1693: Enum."-map/2-lists^map/1-1-"/2
    (elixir 1.15.6) lib/enum.ex:1693: Enum."-map/2-lists^map/1-1-"/2
    (mix 1.15.6) lib/mix/tasks/deps.loadpaths.ex:75: Mix.Tasks.Deps.Loadpaths.deps_check/2

It may be worth investigating why mix ecto.migrate needs to run git, but for now the simplest solution is to manually make sure git is installed using heroku-buildpack-apt, which uses the Aptfile to specify what to install.