fix: slice of struct

[mmatur]

Description

This PR fix an issue with slice of struct.

Paerser was not able to fill correctly the following structs

type Foo struct {
	Values []string
	Bar []Bar
}

type Bar struct {
	Values []string
}

When reading the following configuration, paerser was producing incorrect struct.

Foo:
  Values:
    - 123
    - 456
  Bar:
    - Values:
        - 789
        - 014

Related to traefik/traefik#10996

Co-authored-by: Romain [email protected]

[rtribotte]

LGTM

[nmengin]

LGTM