Change damping_constant property under t_inner property in tardis_example.yml

[atharva-2001]

Is your feature request related to a problem? Please describe.
Reducing the damping_constant property under the t_inner property to 0.5 would cause the simulation to converge faster and would look good when displaying the convergence plots in the documentation.

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Additional context
Before changes

After reducing damping_constant to 0.5