Strip space from pasted text (#1142)

Author: chengfangho

conf.py

@@ -166,6 +166,6 @@ def _asset_hash(path: os.PathLike[str]) -> str:
 
 # Strip the dollar prompt when copying code
 # https://sphinx-copybutton.readthedocs.io/en/latest/use.html#strip-and-configure-input-prompts-for-code-cells
-copybutton_prompt_text = "$"
+copybutton_prompt_text = "$ "
 # https://sphinx-copybutton.readthedocs.io/en/latest/use.html#honor-line-continuation-characters-when-copying-multline-snippets
 copybutton_line_continuation_character = "\\"