Bug#1043301: dh-python should declare Depends python3 >= 3.11

[Tianyu Chen]

Control: reopen -1

Hi Stefano,

I believe dh-python should either declare dependency on python3 >= 3.11, or 
install python3-tomli on python3 << 3.11 and use tomli as fallback when tomllib 
can't be imported.

Tianyu Chen