cmd/git(fix[Git.pull]): Fix --signoff flag spelling

why: The flags were spelled with underscore (--sign_off, --no-sign_off)
but git expects hyphen format (--signoff, --no-signoff).
what:
- Change --sign_off to --signoff
- Change --no-sign_off to --no-signoff

Author: tony

src/libvcs/cmd/git.py

@@ -947,9 +947,9 @@ def pull(
         if no_edit:
             local_flags.append("--no-edit")
         if sign_off:
-            local_flags.append("--sign_off")
+            local_flags.append("--signoff")
         if no_sign_off:
-            local_flags.append("--no-sign_off")
+            local_flags.append("--no-signoff")
         if stat:
             local_flags.append("--stat")
         if no_stat: