Dependabot: `pip-compile` 5.5.0 support

Dependabot version updates now support pip-compile 5.5.0.

Note that with the version update of pip-compile from 5.4.0 to 5.5.0, the formatting of "via" annotations has changed to one dependency per line. This will cause Dependabot to rewrite your requirements.txt file the first time you use the new version.

To enable version updates, check in a dependabot.yml file with the specified package-ecosystem.