Backport !732 “gs-details-page: Enhance the alternates deduplication cycle” to gnome-40
The deduplication works as long as the array doesn't contain the same pointers or when those are not interleaved. Being interleaved it can happen the first occurrence of the second or later instance is skipped due to the array content shift with g_ptr_array_remove(), which removed the first occurrence of the data.
Closes #1192 (closed)
Trivial backport of !732 (merged) to gnome-40
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