`extract_full_summary_from_signature` uses undocumented `Match.regs`

[jiasli]

extract_full_summary_from_signature (added by 430c39e) uses undocumented Match.regs:

knack/knack/introspection.py

Line 22 in e0c1411

summary = lines[:match.regs[0][0]] if match else lines

According to

• https://stackoverflow.com/questions/27537007/alternative-to-regs-attribute-of-match-object-in-re-in-python3
• No mention of match.regs in re documentation python/cpython#62243

it should be replaced by Match.span.

Related: #281