Fix Context in-place mutability bypass via inherited dict methods (#5399)

* opentelemetry-api: Fix Context in-place mutability bypass via inherited dict methods

* Rename context-immutability.fixed to 5399.fixed

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Co-authored-by: Leighton Chen <lechen@microsoft.com>
Co-authored-by: Emídio Neto <9735060+emdneto@users.noreply.github.com>
Co-authored-by: Lukas Hering <40302054+herin049@users.noreply.github.com>
Co-authored-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>