Avoid showing SEO/metadata description on vocab home page

[osma]

Reasons for creating this PR

It was possible for vocabulary descriptions set in the configuration that were intended for SEO / HTML metadata to be shown on vocabulary home page next to the longer description from the concept scheme metadata:

This PR avoids the situation by making the description from the concept scheme override any descriptions defined in the configuration file:

Link to relevant issue(s), if any

• follow-up fix to SEO functionality backport for skosmos 2 #1666

Description of the changes in this PR

• when determining the description to show on the vocabulary home page, prefer the description from the concept scheme metadata (it will override the description set in the configuration file)

Known problems or uncertainties in this PR

Probably the same thing, or something similar, needs to be done in Skosmos 3 as well.

No PHPUnit tests, sorry.

Checklist

• phpUnit tests pass locally with my changes
• I have added tests that show that the new code works, or tests are not relevant for this PR (e.g. only HTML/CSS changes)
• The PR doesn't reduce accessibility of the front-end code (e.g. tab focus, scaling to different resolutions, use of .sr-only class, color contrast)
• The PR doesn't introduce unintended code changes (e.g. empty lines or useless reindentation)

[sonarcloud]

Quality Gate failed

Failed conditions
D Maintainability Rating on New Code (required ≥ A)

See analysis details on SonarCloud

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[joelit]

LGTM