git: Use environment from login shell to search for system git binary, and prefer it to the bundled binary (#39302)

Closes #38571

Release Notes:

- git: Fixed git features not working when git was installed in an
unusual location.

---------

Co-authored-by: Lukas Wirth <me@lukaswirth.dev>

crates/project/src/git_store.rs

@@ -4607,9 +4607,12 @@ impl Repository {
                     log::error!("failed to get working directory environment for repository {work_directory_abs_path:?}");
                     HashMap::default()
                 });
+            let search_paths = environment.get("PATH").map(|val| val.to_owned());
             let backend = cx
                 .background_spawn(async move {
-                    fs.open_repo(&dot_git_abs_path)
+                    let system_git_binary_path = search_paths.and_then(|search_paths| which::which_in("git", Some(search_paths), &work_directory_abs_path).ok())
+                        .or_else(|| which::which("git").ok());
+                    fs.open_repo(&dot_git_abs_path, system_git_binary_path.as_deref())
                         .with_context(|| format!("opening repository at {dot_git_abs_path:?}"))
                 })
                 .await?;

crates/project/src/project_tests.rs

@@ -7797,7 +7797,9 @@ async fn test_staging_random_hunks(
         path!("/dir/.git").as_ref(),
         &[("file.txt", index_text.clone())],
     );
-    let repo = fs.open_repo(path!("/dir/.git").as_ref()).unwrap();
+    let repo = fs
+        .open_repo(path!("/dir/.git").as_ref(), Some("git".as_ref()))
+        .unwrap();
 
     let project = Project::test(fs.clone(), [path!("/dir").as_ref()], cx).await;
     let buffer = project