Pin starlette version

[webb-ben]

Overview

Pin starlette version to pass CI tests

Related Issue / Discussion

Additional Information

Contributions and Licensing

(as per https://github.com/geopython/pygeoapi/blob/master/CONTRIBUTING.md#contributions-and-licensing)

• I'd like to contribute [feature X|bugfix Y|docs|something else] to pygeoapi. I confirm that my contributions to pygeoapi will be compatible with the pygeoapi license guidelines at the time of contribution.
• I have already previously agreed to the pygeoapi Contributions and Licensing Guidelines

[francbartoli]

Hi @webb-ben, may I ask what's the reason to pin it at a specific version?

[webb-ben]

@francbartoli Master CI & all CI fails due to a response from the starlette section of test_api.py. Documented at #1445

[ricardogsilva]

@webb-ben @francbartoli see #1447 for an alternative that focuses on modifying the failing tests instead of pinning starlette - there also a relevant comment on #1445

[webb-ben]

Thanks @ricardogsilva