fix(mapper): mark items that are being fetched as processed (#198)

[neo-reply-lukas]

Mark items that are being fetched as processed. Otherwise, items are fetched multiple times because of async race conditions.

[github-actions[bot]]

:tada: This PR is included in version 10.19.1 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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