For some reason calling UpdateRedgateNugetPackages task no longer creates PR for created/updated branch.
You can look it up by searching for PRs named "Redgate Nuget Package Auto-Update", as I doubt anyone uses non-default PR name.
For me it looks like it stopped creating PR around July 2022, those are two latest PRs that I can see:

Issue source
I stumbled on this as someone reported SQL Source Control's RG Nuget Package Update build failing, so I checked out what it does. It updates pkg-auto-update branch successfully, but there's no PR for it, even though from code it looks like it should create one.