Data issue: Duplicate Carbon Intensity record for 19th April 2021

[sebhulse]

I noticed a duplicate Carbon Intensity record from the /intensity endpoint. Specifically, for 2021-04-19 19:00Z - 19:30Z, there are two records with different values. To reproduce, see here: https://api.carbonintensity.org.uk/intensity/2021-04-19T19:30:00+00:00/2021-04-19T20:00:00+00:00 . This is the only duplicate record I found from 2018-01-01 to 2023-09-19.