[BUG] Internal server error when taking too long to accept/decline grant

[sidvishnoi]

Steps to reproduce

1. Create an outgoing payment grant and reach the /grant-interactions page.
2. Do nothing for long enough (haven't checked what's the timeout for that)
3. Click accept or decline

Expected result

interact.finish.uri (redirect) to be followed with a grant failure indication in URL parameter.

Actual result

A modal with message "Internal server error" is shown.

Screenshots or videos

Additional context

No response

Operating system

Windows, macOS, Linux

Operating system version

No response

Browsers

Chrome, Microsoft Edge, Firefox

Browser version

No response