base: Clone git repo if present instead of rsync

I am guessing I may be one of the first people to try using tmt
with a Rust project. The default for the `cargo` toolchain
is to keep a *lot* of cached incremental data in `target/`.
In my case with bootc, it's currently 20G.

A plain rsync() of this is *incredibly* inefficient. rsync doesn't
even use reflinks if available, though that's a distinct bug.

Change the logic here to do a `git clone -s` which is *way*
more efficient; it properly honors my `.gitignore` which
includes `target/`.

Signed-off-by: Colin Walters <walters@verbum.org>

tmt/base.py

@@ -1796,7 +1796,12 @@ def _initialize_worktree(self) -> None:
 
         # Sync metadata root to the worktree
         self.debug(f"Sync the worktree to '{self.worktree}'.", level=2)
-        self.run(Command("rsync", "-ar", "--exclude", ".git", f"{tree_root}/", self.worktree))
+        # If we're in a git repository, we just clone it so that we correctly
+        # honor .gitignore, etc.
+        if os.path.isdir(f"{tree_root}/.git"):
+            self.run(Command("git", "clone", "-s", tree_root, self.worktree))
+        else:
+            self.run(Command("rsync", "-ar", "--exclude", ".git", f"{tree_root}/", self.worktree))
 
     def _initialize_data_directory(self) -> None:
         """