Add .python-version file
Add .python-version file

* test whether this will persuade dependabot to use the correct version
* 3.8.6 because that appears to be what is currently used in production

ebmdatalab/openprescribing,annapowellsmith/openpresc,ebmdatalab/openprescribing,annapowellsmith/openpresc,ebmdatalab/openprescribing,annapowellsmith/openpresc,annapowellsmith/openpresc,ebmdatalab/openprescribing