fix: add --recurse-submodules to checkout module (#439)

Co-authored-by: Bartosz Sokorski <b.sokorski@gmail.com>

src/poetry/core/vcs/git.py

@@ -292,7 +292,7 @@ def checkout(self, rev: str, folder: Path | None = None) -> str:
 
         self._check_parameter(rev)
 
-        args += ["checkout", rev]
+        args += ["checkout", "--recurse-submodules", rev]
 
         return self.run(*args)