Tests: update navbar in visual modal test

[julien-deramond]

Description

This PR updates the navbar used in our modal visual test which still use old .navbar-full and .hidden-lg-up classes, and so never render the content of the navbar.

For context, .hidden-lg-up and .navbar-full were removed after v4.0.0 alpha versions.

Their usage was the following:

The .hidden-*-up classes hide the element when the viewport is at the given breakpoint or wider. For example, .hidden-md-up hides an element on medium, large, and extra-large viewports.

Corresponding code in bootstrap.css in v4.0.0-alpha.5

@media (min-width: 992px) {
  .hidden-lg-up {
    display: none !important;
  }
}

that I've changed to our .navbar-expand-lg which does the same thing:

@media (min-width: 992px) {
.navbar-expand-lg .navbar-toggler {
    display: none;
  }
}

Regarding .navbar-full, IMO we can just drop it as it's already handled by our .navbar-* classes:

.navbar-full {
  z-index: 1000;
}

@media (min-width: 576px) {
  .navbar-full {
    border-radius: 0;
  }
}

The global modification of the navbar follows our current navbar documentation and usage.

Type of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• (N/A) My change introduces changes to the documentation
• (N/A) I have updated the documentation accordingly
• (N/A) I have added tests to cover my changes
• All new and existing tests passed

Live preview

• Locally: http://localhost:8008/js/tests/visual/modal.html