Fix Labeller config file to new v5 syntax

[karianna]

Somewhere along the lines we moved to v5 which has totally new syntax actions/labeler#712

[sxa]

Presumably this is the cause of the labeler failures on every PR at the moment?

The configuration file (path: .github/labeler.yml) was not found locally, fetching via the api
Error: Error: found unexpected type for label 'ghActions' (should be array of config options)
Error: found unexpected type for label 'ghActions' (should be array of config options)

[karianna]

#872 attempts to fix this