Add --include-untracked flag to stash show command (#3932)

- **PR Description**

This PR fixes #3931 by adding `--include-untracked` to `git stash show`
command. Untracked stashed file diff is now shown in the main view.

![before this
PR](https://github.com/user-attachments/assets/81097c71-3764-4467-a960-a87c51921139)
*Before: the untracked stashed file is not shown in lazygit*.

![after this
PR](https://github.com/user-attachments/assets/4aafd5f6-5305-4f9b-9068-1570d22e755c)
*After: the untracked stashed file diff is shown in lazygit*.

## One Issue

This PR does not fix the fact that untracked stashed files are not shown
in the list of files in the "Stash" panel when entering a stash entry, I
could not find an easy way to make them appear there.

* [x] Cheatsheets are up-to-date (run `go generate ./...`)
* [x] Code has been formatted (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#code-formatting))
* [x] Tests have been added/updated (see
[here](https://github.com/jesseduffield/lazygit/blob/master/pkg/integration/README.md)
for the integration test guide)
* [x] Text is internationalised (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#internationalisation))
* [ ] If a new UserConfig entry was added, make sure it can be
hot-reloaded (see
[here](https://github.com/jesseduffield/lazygit/blob/master/docs/dev/Codebase_Guide.md#using-userconfig))
* [ ] Docs have been updated if necessary
* [x] You've read through your own file changes for silly mistakes etc

Author: jesseduffield

Diff for: pkg/commands/git_commands/stash.go

@@ -81,9 +81,11 @@ func (self *StashCommands) Hash(index int) (string, error) {
 }
 
 func (self *StashCommands) ShowStashEntryCmdObj(index int) oscommands.ICmdObj {
+	// "-u" is the same as "--include-untracked", but the latter fails in older git versions for some reason
 	cmdArgs := NewGitCmd("stash").Arg("show").
 		Arg("-p").
 		Arg("--stat").
+		Arg("-u").
 		Arg(fmt.Sprintf("--color=%s", self.UserConfig().Git.Paging.ColorArg)).
 		Arg(fmt.Sprintf("--unified=%d", self.AppState.DiffContextSize)).
 		ArgIf(self.AppState.IgnoreWhitespaceInDiffView, "--ignore-all-space").

Diff for: pkg/commands/git_commands/stash_test.go

@@ -113,31 +113,31 @@ func TestStashStashEntryCmdObj(t *testing.T) {
 			contextSize:         3,
 			similarityThreshold: 50,
 			ignoreWhitespace:    false,
-			expected:            []string{"git", "-C", "/path/to/worktree", "stash", "show", "-p", "--stat", "--color=always", "--unified=3", "--find-renames=50%", "stash@{5}"},
+			expected:            []string{"git", "-C", "/path/to/worktree", "stash", "show", "-p", "--stat", "-u", "--color=always", "--unified=3", "--find-renames=50%", "stash@{5}"},
 		},
 		{
 			testName:            "Show diff with custom context size",
 			index:               5,
 			contextSize:         77,
 			similarityThreshold: 50,
 			ignoreWhitespace:    false,
-			expected:            []string{"git", "-C", "/path/to/worktree", "stash", "show", "-p", "--stat", "--color=always", "--unified=77", "--find-renames=50%", "stash@{5}"},
+			expected:            []string{"git", "-C", "/path/to/worktree", "stash", "show", "-p", "--stat", "-u", "--color=always", "--unified=77", "--find-renames=50%", "stash@{5}"},
 		},
 		{
 			testName:            "Show diff with custom similarity threshold",
 			index:               5,
 			contextSize:         3,
 			similarityThreshold: 33,
 			ignoreWhitespace:    false,
-			expected:            []string{"git", "-C", "/path/to/worktree", "stash", "show", "-p", "--stat", "--color=always", "--unified=3", "--find-renames=33%", "stash@{5}"},
+			expected:            []string{"git", "-C", "/path/to/worktree", "stash", "show", "-p", "--stat", "-u", "--color=always", "--unified=3", "--find-renames=33%", "stash@{5}"},
 		},
 		{
 			testName:            "Default case",
 			index:               5,
 			contextSize:         3,
 			similarityThreshold: 50,
 			ignoreWhitespace:    true,
-			expected:            []string{"git", "-C", "/path/to/worktree", "stash", "show", "-p", "--stat", "--color=always", "--unified=3", "--ignore-all-space", "--find-renames=50%", "stash@{5}"},
+			expected:            []string{"git", "-C", "/path/to/worktree", "stash", "show", "-p", "--stat", "-u", "--color=always", "--unified=3", "--ignore-all-space", "--find-renames=50%", "stash@{5}"},
 		},
 	}