[pyupgrade] Add fix safety section to docs (UP030)

[Kalmaegi]

Summary

add fix safety section to format_literals, for #15584

[github-actions]

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[ntBre]

Thanks! This was quite a tricky one, but I think I came up with a scenario where the rule is definitely unsafe. What do you think?

[Kalmaegi]

I tested it again, and currently, sometimes the annotations are swapped, while other times they are not. There might be errors in cases where swapping occurs, but I think these are rare edge cases.
before:

def take_two(x: int, y: int) -> int:
    return x + y

def take_one(x: int) -> int:
    return x + 1

"{1}, {0}".format( # comment 1
    take_two(1, # comment 2
    2), # comment 3 
    take_one(1),
)

after:

def take_two(x: int, y: int) -> int:
    return x + y

def take_one(x: int) -> int:
    return x + 1

"{}, {}".format( # comment 1
    take_one(1), # comment 3 
take_two(1,  # comment 2
    2), 
)

[ntBre]

Very nice, thanks!