[prettier-plugin-toml]: do not add tailing comma to one-line object

[trim21]

I have a one-line object

before

uvicorn = [
    { version = "^0.29.0", platform = 'linux', extras = [ 'standard' ] },
    { version = "^0.29.0", platform = 'win32' },
]

after

uvicorn = [
    { version = "^0.29.0", platform = 'linux', extras = [
        'standard',
    ] },
    { version = "^0.29.0", platform = 'win32' },
]

this doesn't look pretty...