Incomplete inline tables should say either key or `}` is needed

[epage]

Cargo has a test case with a multi-line inline table. The error message is

  TOML parse error at line 8, column 27
    |
  8 |                 native = {
    |                           ^
  Unexpected `
  `
  Expected `key`

A } is also expected.

See https://github.com/rust-lang/cargo/pull/10086

[epage]

Related case: have some key-value pairs before the line line