Update GitLab Disability and Neurodivergence TMRG references and wording after rename

Why is this change being made?

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This MR updates the company website to reflect the renaming the DiversABILITY TMRG to GitLab Disability and Neurodivergence and to better reflect self-identification and more inclusive language for disabled and/or neurodivergent team members.

Tagging @gitlab-com/ceo-chief-of-staff-team for the CODEOWNERS update to reflect the current TMRG leads.

Author and Reviewer Checklist

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