Bump starlette from 0.27.0 to 0.28.0

Bumps [starlette](https://github.com/encode/starlette) from 0.27.0 to 0.28.0.
- [Release notes](https://github.com/encode/starlette/releases)
- [Changelog](https://github.com/encode/starlette/blob/master/docs/release-notes.md)
- [Commits](encode/starlette@0.27.0...0.28.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

poetry.lock

@@ -64,7 +64,7 @@ django = {version = ">=3.0", optional = true}
 falcon = {version = ">=3.0", optional = true}
 flask = {version = "*", optional = true}
 aiohttp = {version = ">=3.0", optional = true}
-starlette = {version = ">=0.26.1,<0.28.0", optional = true}
+starlette = {version = ">=0.26.1,<0.29.0", optional = true}
 isodate = "*"
 more-itertools = "*"
 parse = "*"