Airnode attempts to fulfil the same requests multiple times every now and then

[aTeoke]

Description

When having 2 providers Airnode doesn't get VM exception / static call errors / nonce errors and sends fulfillment transactions thinking they will succeed and they revert on-chain

Version

Airnode 0.10 and up

Discussion here: https://api3workspace.slack.com/archives/C02AYRX8D89/p1680274185877999

[bdrhn9]

I suspect that using both Skipping API call and cacheResponses features at the same time can cause this issue.

[Siegrift]

Waiting until we agree internally on the resolution.

[bbenligiray]

Summarizing https://api3workspace.slack.com/archives/C02AYRX8D89/p1681907159870799

This is most likely a finality problem regarding using very low minConfirmations on testnets. The diagnosis was difficult because this manifested with another bug, #1749

In summary,

• @aTeoke This issue can be closed. There's nothing particularly wrong about Airnode v0.9 and later versions.
• I uncovered a somewhat serious implementation error while debugging this Airnode attemps to fail the request when the sponsor wallet is invalid #1749
• I uncovered a potential security issue while debugging this Airnode forwards blockchain provider error messages as is #1750