Prep for v1.38.1

[odow]

Basic

• version field of Project.toml has been updated
  - If a breaking change, increment the MAJOR field and reset others to 0
  - If adding new features, increment the MINOR field and reset PATCH to 0
  - If adding bug fixes or documentation changes, increment the PATCH field

Documentation

• Add a new entry to docs/src/changelog.md, following existing style

Tests

• https://github.com/jump-dev/MathOptInterface.jl/actions/runs/14253627565
• https://github.com/jump-dev/MathOptInterface.jl/actions/runs/14298510627
• If new tests were added, ensure that MOI.Test.version_added is implemented.

[odow]

So I think ForwardDiff@1 actually broke JuMP: https://github.com/jump-dev/MathOptInterface.jl/actions/runs/14230566003/job/39880201946

[odow]

Requires #2708

[odow]

Looks like the cause was JuliaDiff/ForwardDiff.jl#739

[odow]

Merging and tagging because this includes ForwardDiff@1 which a few people have asked me about.