Add test to auto-amend a commit after pressing e on it

Auto-amending is a little-known feature of git that is very convenient once you
know it: whenever you stop at a commit marked with `edit` in an interactive
rebase, you can make changes and stage them, and when you continue the rebase
they automatically get amended to the commit you had stopped at. This is so
convenient because making changes to a commit is one of the main reasons why you
edit a commit.

Unfortunately this currently doesn't work in lazygit because we don't actually
use `edit` to stop at the first commit (instead, we add a `break` todo after it,
which doesn't have the auto-amend functionality).

We'll improve this later in this branch.

pkg/integration/tests/test_list.go

@@ -210,6 +210,7 @@ var tests = []*components.IntegrationTest{
 	interactive_rebase.DropCommitInCopiedBranchWithUpdateRef,
 	interactive_rebase.DropTodoCommitWithUpdateRef,
 	interactive_rebase.DropWithCustomCommentChar,
+	interactive_rebase.EditAndAutoAmend,
 	interactive_rebase.EditFirstCommit,
 	interactive_rebase.EditLastCommitOfStackedBranch,
 	interactive_rebase.EditNonTodoCommitDuringRebase,