Git on main thread (#26573)

This moves spawning of the git subprocess to the main thread. We're not
yet
sure why, but when we spawn a process using GCD's background queues,
sub-processes like git-credential-manager fail to open windows.

This seems to be fixable either by using the main thread, or by using a
standard background thread,
but for now we use the main thread.


Release Notes:

- Git: Fix git-credential-manager

---------

Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>
Co-authored-by: Kirill Bulatov <mail4score@gmail.com>

crates/remote_server/src/remote_editing_tests.rs

@@ -1361,7 +1361,7 @@ async fn test_remote_git_branches(cx: &mut TestAppContext, server_cx: &mut TestA
 
     assert_eq!(&remote_branches, &branches_set);
 
-    cx.update(|cx| repository.read(cx).change_branch(new_branch))
+    cx.update(|cx| repository.read(cx).change_branch(new_branch.to_string()))
         .await
         .unwrap()
         .unwrap();
@@ -1383,15 +1383,23 @@ async fn test_remote_git_branches(cx: &mut TestAppContext, server_cx: &mut TestA
     assert_eq!(server_branch.name, branches[2]);
 
     // Also try creating a new branch
-    cx.update(|cx| repository.read(cx).create_branch("totally-new-branch"))
-        .await
-        .unwrap()
-        .unwrap();
+    cx.update(|cx| {
+        repository
+            .read(cx)
+            .create_branch("totally-new-branch".to_string())
+    })
+    .await
+    .unwrap()
+    .unwrap();
 
-    cx.update(|cx| repository.read(cx).change_branch("totally-new-branch"))
-        .await
-        .unwrap()
-        .unwrap();
+    cx.update(|cx| {
+        repository
+            .read(cx)
+            .change_branch("totally-new-branch".to_string())
+    })
+    .await
+    .unwrap()
+    .unwrap();
 
     cx.run_until_parked();