pkg/query: Data races

[metalmatze]

CI runs fail to run make test ENABLE_RACE=yes due to race conditions.
Our CI doesn't always catch this, but I can consistently reproduce it on a beefier machine locally.
go test -race -tags assert -v ./pkg/query scopes to test the specific package.

It seems to already have been on https://github.com/parca-dev/parca/releases/tag/v0.20.0; however, not on https://github.com/parca-dev/parca/releases/tag/v0.19.0.

git bisect said it was this commit that broke things: 44bc42e
That is quite odd as this commit only ran buf generate.

I need more time to investigate when this started happening and then find out why.
If you have an idea, feel free to share.