[web] Update test skip description.

[ferhatb]

Description

Web engine doesn't use Http to load and decode. It uses image element. Web itself doesn't report progress due to security implications (exposing size of remote files).

This PR updates the skip description.

Related Issues

Addresses: #56317

Tests

Test case updated.

Checklist

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• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
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• I updated/added relevant documentation (doc comments with ///).
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Breaking Change

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• Yes, this is a breaking change. If not, delete the remainder of this section.
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[Piinks]

LGTM! Thanks! Can we close the issue then?