Serialize GraphQL & EdgeQL tests over HTTP.
Serialize GraphQL & EdgeQL tests over HTTP.

Context: every GraphQL or EdgeQL Port has a concurrency setting, which
corresponds to a number of Python compiler processes run for that port.
Before this commit we would try to parallelize all GraphQL and EdgeQL
HTTP tests, which ended up un creating too many GraphQL/EdgeQL ports.
That bumped the number of open FDs in the main DB server process to
unreasonably high numbers.

edgedb/edgedb,edgedb/edgedb,edgedb/edgedb