Remove vertical borders for easier copying

ci/diff.py

@@ -9,6 +9,7 @@
 from itertools import zip_longest
 from typing import Any, Iterable
 
+from rich import box
 from rich.console import Console, Group
 from rich.markup import escape
 from rich.panel import Panel
@@ -98,7 +99,7 @@ def get_diff(expected: list[str], result: list[str]) -> Group:
     """Print a diff between two lists of strings."""
     gen = difflib.ndiff(expected, result)
     lines = fmt_lines(gen)
-    return Group(DIFF_HEADER, Panel(lines))
+    return Group(DIFF_HEADER, Panel(lines, box=box.HORIZONTALS))
 
 
 class Choice(StrEnum):