git: Improve error messages (#35946)

Release Notes:

- Improved git error messages

Includes stderr in the error message for git commands, provides better
output for things like errors when switching branches.

Before:
<img width="702" height="330" alt="image"
src="https://github.com/user-attachments/assets/f32402ae-b85c-4b0b-aae8-789607e8ec9e"
/>

After:
<img width="650" height="575" alt="image"
src="https://github.com/user-attachments/assets/308dbe3c-1ff9-40b9-a187-1e12d2488c80"
/>

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/workspace/src/notifications.rs

@@ -1077,8 +1077,13 @@ where
             if let Err(err) = result.as_ref() {
                 log::error!("{err:?}");
                 if let Ok(prompt) = cx.update(|window, cx| {
+                    let mut display = format!("{err}");
+                    if !display.ends_with('\n') {
+                        display.push('.');
+                        display.push(' ')
+                    }
                     let detail =
-                        f(err, window, cx).unwrap_or_else(|| format!("{err}. Please try again."));
+                        f(err, window, cx).unwrap_or_else(|| format!("{display}Please try again."));
                     window.prompt(PromptLevel::Critical, &msg, Some(&detail), &["Ok"], cx)
                 }) {
                     prompt.await.ok();