Unable to use CSV file as ComplexInput

# Description
When using a `ComplexInput` with `support_formats=[Format("text/csv", extension=".csv")]`, `pywps` is unable to read the csv file when the process is running from a docker container.

# Environment

- operating system: `ubuntu-20.04`
- Python version: `3.8`
- PyWPS version: `4.2.10`
- source/distribution
- [ ] git clone
- [ ] Debian
- [x] PyPI
- [ ] zip/tar.gz
- [ ] other (please specify):

# Additional Information
We have checked that the `csv` with the `mimetypes` package:
```python3
>>> mimetypes.guess_type("/path/to/csv")
('text/csv', None)
```
There is no encoding listed and by the time the input is accesses with a `csv` reader it is a bytes stream (with an illegal start byte).