bug#63959: python-mode does not keep indentation in square brackets []

[Konstantin Kharlamov]

Usually in programming modes, when previous indentation is kind of "special",
the new lines should keep the indentation from the previous line. However, it
doesn't work in this case.


# Steps to reproduce

1. Create file `test.py` with following content:

    for infix in [ # some description
                  "_cdata", "_cmeta", "_corig", "_cpool", "_cvol", "_wcorig",
                  "indentation is broken here", "bar"]:
        print(infix)

2. Open it as `emacs -Q test.py`
3. Put a caret on the 3rd line (which says "indentation is broken"
4. Press TAB


## Expected

Indentation won't change

## Actual

The line goes back by 4 spaces or so

# Additional information

emacs version: compiled from latest git a week ago, commit 5cace109d2b