Git uncommit warning (#25977)

Adds a prompt when clicking the uncommit button when the current commit
is already present on a remote branch:

![screenshot showing
prompt](https://github.com/user-attachments/assets/d6421875-588e-4db0-aee0-a92f36bce94b)

Release Notes:

- N/A

---------

Co-authored-by: Conrad <conrad@zed.dev>

crates/proto/src/proto.rs

@@ -454,6 +454,8 @@ messages!(
     (RemoteMessageResponse, Background),
     (GitCreateBranch, Background),
     (GitChangeBranch, Background),
+    (CheckForPushedCommits, Background),
+    (CheckForPushedCommitsResponse, Background),
 );
 
 request_messages!(
@@ -598,6 +600,7 @@ request_messages!(
     (Pull, RemoteMessageResponse),
     (GitCreateBranch, Ack),
     (GitChangeBranch, Ack),
+    (CheckForPushedCommits, CheckForPushedCommitsResponse),
 );
 
 entity_messages!(
@@ -701,6 +704,7 @@ entity_messages!(
     Pull,
     GitChangeBranch,
     GitCreateBranch,
+    CheckForPushedCommits,
 );
 
 entity_messages!(