dotnet-format not being recognised when run via gitlab runner

I've extracted the key lines from my ci-cd script. I'm very confused.

```
$ dotnet tool update -g dotnet-format
Tool 'dotnet-format' was reinstalled with the latest stable version (version '4.1.131201').
$ dotnet-format
'dotnet-format' is not recognized as an internal or external command,
operable program or batch file.
```

I've logged into my build server, changed my user to `NT AUTHORITY\SYSTEM` that the Gitlab runner operates under, and run `dotnet-format` and it works.

Any help on where I could proceed with my debugging would be much appreciated.