Michael Schmoock f11c9ca6ec workflows: remove use-feature=in-tree-build ...

Using `--use-feature=in-tree-build` is no longer needed for recent pip versions,
doing so raised:

```
option --use-feature: invalid choice: 'in-tree-build' (choose from 'fast-deps', 'truststore', 'no-binary-enable-wheel-cache')
```

2023-01-01 16:04:20 +01:00

..

main.yml

workflows: remove use-feature=in-tree-build

2023-01-01 16:04:20 +01:00