Bump starlette from 0.38.0 to 0.39.0 (#260)

Bumps [starlette](https://github.com/encode/starlette) from 0.38.0 to 0.39.0.
- [Release notes](https://github.com/encode/starlette/releases)
- [Changelog](https://github.com/encode/starlette/blob/master/docs/release-notes.md)
- [Commits](encode/starlette@0.38.0...0.39.0)

---
updated-dependencies:
- dependency-name: starlette
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

pyproject.toml

@@ -9,7 +9,7 @@ repository = "https://github.com/aogier/starlette-authlib"
 [tool.poetry.dependencies]
 python = "^3.8"
 authlib = "<1.4"
-starlette = "<0.39"
+starlette = "<0.40"
 
 [tool.poetry.group.dev.dependencies]
 autoflake = "<2.3"