[test] fix side-effect due to repeated fields

[picnixz]

Closes #12121.

The side-effect can be solved in two manners:

• Remove the duplicated entries in field-role.rst.
• Assume that semicolon.rst and index.rst were the only files meant to be fixed.

@jayaddison Which one do you prefer (I assumed to only use two files since there are other conflicting entries I think with other pairs of files and at least we know which files are being used).

[jayaddison]

Closes #12121.

The side-effect can be solved in two manners:

* Remove the duplicated entries in `field-role.rst`.

* Assume that `semicolon.rst` and `index.rst` were the only files meant to be fixed.

@jayaddison Which one do you prefer (I assumed to only use two files since there are other conflicting entries I think with other pairs of files and at least we know which files are being used).

I think I prefer the first approach, and the reason: the second case performs a 'different build', doesn't it? (doesn't share the same config)

[picnixz]

I would also go for the first one, but... we are also suppressing some warnings as well, especially those concerning 'orphan' documents not marked as orphan.

I'll think a bit more (this one is not pressing) about which direction to take (since it could affect other tests using the same files).