cmd/git(fix[Git.clone]): Fix reference_if_able flag name

why: The parameter was emitting --reference instead of --reference-if-able,
which has different semantics (--reference fails if local repo is missing,
--reference-if-able silently skips).
what:
- Change ["--reference", reference_if_able] to ["--reference-if-able", ...]

Author: tony

src/libvcs/cmd/git.py

@@ -371,7 +371,7 @@ def clone(
         if reference is not None:
             local_flags.extend(["--reference", reference])
         if reference_if_able is not None:
-            local_flags.extend(["--reference", reference_if_able])
+            local_flags.extend(["--reference-if-able", reference_if_able])
         if server_option is not None:
             local_flags.append(f"--server-option={server_option}")
         if jobs is not None: