CompatHelper: bump compat for HTTP to 2, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the HTTP package from 1 to 1, 2.
This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

[kalidke]

Triaged 2026-06-05. This is not a drop-in compat bump — HTTP.jl 2.0 is a breaking API change. CI fails across all Julia versions with:

MethodError: no method matching serve!(::handler, ::String, ::Int64; stream::Bool)
@ ModelContextProtocol src/transports/http.jl:561

HTTP.jl 2.0 changed the HTTP.serve! signature (and likely other Request/Response/streaming APIs the transport relies on). HTTP 1.x remains fully supported and is the resolved version today.

Holding this until a dedicated HTTP 2 migration PR updates src/transports/http.jl and re-verifies the full HTTP + SSE suite against HTTP 2. Not merging the bare compat widening, since it would let the resolver pick a broken HTTP 2.