git_panel: Fix amend check (#29059)

Smit Barmase created 

`is_some` -> `is_none` 

Release Notes:

- N/A

Change summary

crates/git_ui/src/commit_modal.rs | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

Detailed changes

crates/git_ui/src/commit_modal.rs 🔗 

@@ -545,7 +545,7 @@ impl CommitModal {
             .active_repository
             .as_ref()
             .and_then(|repo| repo.read(cx).head_commit.as_ref())
-            .is_some()
+            .is_none()
         {
             return;
         }