Prep for v1.50.0

[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/22469911691
• https://github.com/jump-dev/MathOptInterface.jl/actions/runs/22552654022
• https://github.com/jump-dev/MathOptInterface.jl/actions/runs/22651889251
• If new tests were added, ensure that MOI.Test.version_added is implemented.

[odow]

Okay, this is now ready.

[odow]

It's baaaack. But now in the reverse case. I don't know what's going on. Seems like cholesky is super flakey between Julia versions.