git: Use correct file mode when staging (#41900)

Closes #28667

Release Notes:

- Fixed git not preserving file mode when committing. Now if an input file is executable it will be preserved when committed with Zed.

---------

Signed-off-by: 11happy <soni5happy@gmail.com>
Signed-off-by: 11happy <bhuminjaysoni@gmail.com>
Co-authored-by: Jakub Konka <kubkon@jakubkonka.com>

Cargo.lock

@@ -6406,6 +6406,7 @@ dependencies = [
  "git",
  "gpui",
  "ignore",
+ "is_executable",
  "libc",
  "log",
  "notify 8.2.0",
@@ -8436,6 +8437,15 @@ dependencies = [
  "once_cell",
 ]
 
+[[package]]
+name = "is_executable"
+version = "1.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "baabb8b4867b26294d818bf3f651a454b6901431711abb96e296245888d6e8c4"
+dependencies = [
+ "windows-sys 0.60.2",
+]
+
 [[package]]
 name = "is_terminal_polyfill"
 version = "1.70.1"