chore(deps-dev): bump pydantic-openapi-helper from 0.2.4 to 0.2.6

Bumps [pydantic-openapi-helper](https://github.com/ladybug-tools/pydantic-openapi-helper) from 0.2.4 to 0.2.6.
- [Release notes](https://github.com/ladybug-tools/pydantic-openapi-helper/releases)
- [Changelog](https://github.com/ladybug-tools/pydantic-openapi-helper/blob/master/.releaserc.json)
- [Commits](ladybug-tools/pydantic-openapi-helper@v0.2.4...v0.2.6)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

dev-requirements.txt

@@ -1,4 +1,4 @@
-pydantic_openapi_helper==0.2.4
+pydantic_openapi_helper==0.2.6
 coverage==5.5
 coveralls==2.2.0
 pytest==6.2.2