That's been there since lockdowns started in 2020 hasn't it? Private property round the ground and they've been restricting access. Think it was first put in place for the matches played without fans to keep them away. See the signs about covid checks on either side? They were still in place...
This is why I've already got a paper copy of my vaccination certificate:
https://www.nhs.uk/conditions/coronavirus-covid-19/covid-pass/get-your-covid-pass-letter/