fix(ui5-media-gallery): acc findings fixed

[PetyaMarkovaBogdanova]

4) MediaGallery (22 failing)

• Repeated continuum violations, including:
• LI with role="option" missing aria-checked (ID 1079).
• UL child-structure violation for list semantics (ID 246).
• Failing examples include thumbnail options and overflow scenarios.

MediaGallery	option items missing required state	ID 1079: LI role option missing aria-checked	Option semantics implemented but selection state attribute omitted on some items	Likely real	High	Provide consistent state attribute where role requires it, or switch to correct role-state pair	All option-like items expose required state attributes consistently
MediaGallery	UL child-structure violation	ID 246 list child structure	Children inside list container are not valid list children in overflow/thumbnail variants	Likely real	High	Normalize list markup so only valid child structure exists in all modes	Thumbnail and overflow DOM both satisfy list parent-child constraints

[ui5-webcomponents-bot]

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