Update doc with MATLAB support notice

[davidbuzinski]

Hi,

The method used to install and license the matlab language on Travis CI is out of date, and will no longer be supported in releases following R2024a. It will continue to work indefinitely for R2024a and earlier releases, but we would like to add a notice that it will no longer get the "latest" releases of MATLAB in the future.

Please feel free to reach out with additional questions or comments.

Thanks,
David

[cceneag]

This pull request updates the documentation for MATLAB language support in the user/languages/matlab.md file. The changes reflect the deprecation of MATLAB builds and clarify the limitations on supported releases.

Updates to MATLAB support documentation:

• Removed the "Support" section linking to MathWorks' email, indicating a shift away from active support for MATLAB builds. ([user/languages/matlab.mdL17](https://github.com/travis-ci/docs-travis-ci-com/pull/3362/files#diff-6d1b3b41e4776eac7e35a6e40b84689495658f3f5fd4a983fa1fbdc10e0f2e6dL17))
• Updated the warning to state that MATLAB builds are no longer supported, are limited to public projects in Linux environments, and that releases beyond R2024a are unavailable. ([user/languages/matlab.mdL28-L40](https://github.com/travis-ci/docs-travis-ci-com/pull/3362/files#diff-6d1b3b41e4776eac7e35a6e40b84689495658f3f5fd4a983fa1fbdc10e0f2e6dL28-L40))