Fix umbrella QA project count after multirate split

[ChrisRackauckas-Claude]

Ignore this PR until it has been reviewed by @ChrisRackauckas.

What changed and why

Update the umbrella QA guard from 39 to 40 projects. OrdinaryDiffEqMultirateImplicit, added by #4115, depends on OrdinaryDiffEqCore and declares a MuladdMacro compat floor, so it is intentionally included by this check.

A scripted bisect identified 4bf7627 as the first failing commit. Its parent produces 39 matching projects; that commit adds OrdinaryDiffEqMultirateImplicit as the 40th. I found no existing issue or open PR for this failure.

Verification

Failing before the fix on clean upstream/master:

$ GROUP=QA julia --project -e 'using Pkg; Pkg.test()'
PureKLU-compatible MuladdMacro floors: Test Failed at test/qa/qa_tests.jl:20
  Expression: length(projects) == 39
   Evaluated: 40 == 39
Test Summary:           | Pass  Fail  Total
Quality Assurance Tests |   89     1     90
ERROR: Package OrdinaryDiffEq errored during testing

The same failure occurred in the introducing PR's Actions job: https://github.com/SciML/OrdinaryDiffEq.jl/actions/runs/31338186806/job/93308671126.

Passing after the fix:

$ GROUP=QA julia --project -e 'using Pkg; Pkg.test()'
Test Summary:           | Pass  Total   Time
Quality Assurance Tests |   90     90  11.5s
     Testing OrdinaryDiffEq tests passed

Formatting and spelling:

$ julia -m Runic --check test/qa/qa_tests.jl
$ typos test/qa/qa_tests.jl
$ git diff --check

All three exited successfully with no output.

Not verified

I did not run GROUP=Everything, GPU tests, or downstream groups. This changes only the expected size of the project set already exercised by the QA group. No docs or public API were changed, so the docs build was not run.