concurrent.futures is missing link to InterpreterPoolExecutor sources

[ojii]

Documentation

https://docs.python.org/3.14/library/concurrent.futures.html only links process.py and thread.py, but not interpreter.py.

Linked PRs

• gh-133641: Add missing source link to concurrent.futures docs #133642
• [3.14] gh-133641: Doc: Add missing source link in concurrent.futures (GH-133642) #133643