src/sage_docbuild/conf.py: Fix up copybutton config

Author: Matthias Koeppe

src/sage_docbuild/conf.py

@@ -259,7 +259,8 @@ def set_intersphinx_mappings(app, config):
 # https://sphinx-copybutton.readthedocs.io/en/latest/use.html
 copybutton_prompt_text = r"sage: |[.][.][.][.]: |\$ "
 copybutton_prompt_is_regexp = True
-copybutton_exclude = '.linenos, .gp, .c'  # exclude comments
+copybutton_exclude = '.linenos, .c1'  # exclude single comments (in particular, # optional!)
+copybutton_only_copy_prompt_lines = True
 
 # Options for HTML output
 # -----------------------