[sqlalchemy] Return 404 for missing collection on /items

[gadomski]

Related Issue(s):

• Closes Request to /collection/<missing>/items returns 200 #120

Description:

#120 was already fixed for pgstac but needed the fix for sqlalchemy. Planetary Computer check:

$ curl -i https://planetarycomputer.microsoft.com/api/stac/v1/collections/not-a-collection/items
HTTP/2 404 
content-length: 88
content-type: application/json
strict-transport-security: max-age=15724800; includeSubDomains
access-control-allow-origin: *
access-control-allow-credentials: true
x-cache: CONFIG_NOCACHE
x-azure-ref: 03MjrYwAAAAAJokhog0B4SJ7f/1kQix/yV1NURURHRTAxMTkAOTI3YWJmYTYtMTlmNi00YWYxLWEwOWQtYzk1OWQ5YTFlNjQ0
date: Tue, 14 Feb 2023 17:46:04 GMT

{"code":"NotFoundError","description":"No collection with id 'not-a-collection' found!"}

PR Checklist:

• Code is formatted and linted (run pre-commit run --all-files)
• Tests pass (run make test)
• Documentation has been updated to reflect changes, if applicable, and docs build successfully (run make docs)
• Changes are added to the CHANGELOG.