Fix # fmt: skip on the last line of a multi-line conditional expression in brackets - #5647

Description

When a conditional expression inside brackets spans several lines and # fmt: skip is on its last line, Black produces invalid code:

x = (
    a
    if c else d,  # fmt: skip
    e,
)

error: cannot format repro.py: INTERNAL ERROR: ... produced invalid code: cannot parse: 5:6:         ) e,

With --fast it's written out silently; a variant like a # comment / + b if c else d, # fmt: skip / (e), turns the tuple into a call: (a ... else d, # fmt: skip\n)(e).

# fmt: skip hides only the code on its own line (if c else d,), so that hidden code ends the test node and also takes the comma after it. visit_test then wraps the node in invisible parentheses and the closing one lands after the comma. #5464 fixed the case where the whole ternary is on the skipped line; this is the multi-line one.

visit_test now skips the invisible parentheses when the node's last leaf is code hidden by # fmt: skip, like the existing check for hidden code at the start. Three multi-line cases added to fmtskip_conditional_in_brackets.py; they fail on main and pass with the change.

The same thing still happens under --preview for a dict value via wrap_long_dict_values_in_parens; I left that alone since #5627 is reworking that code.

Checklist - did you ...

• Implement any code style changes under the --preview style, following the stability policy?
• Add an entry in CHANGES.md if necessary?
• Add / update tests if necessary?
• Add new / update outdated documentation?

I used Claude Code to write this change.