Doctest line numbers should be corrected to the failing line, not the start of the test

[joshka]

In the following test failure output, the error is on line 115, not 104. 104 is the start of the example block

running 28 tests
test ratatui-macros/src/lib.rs - (line 104) ... FAILED

...

failures:

---- ratatui-macros/src/lib.rs - (line 104) stdout ----
error: expected one of `,`, `.`, `?`, `]`, or an operator, found `;`
  --> ratatui-macros/src/lib.rs:115:6

...

failures:
    ratatui-macros/src/lib.rs - (line 104)

[Vrajs16]

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