theme: dark option not working as expected

[eduardofesilva]

Hi, The option theme: dark is not working as expected to generate reports for Github dark mode. All the images rendered are still considering the light mode which does not allow us to visualize properly the X and Y title for each one of the graphs generated by the telemetry report

[massongit]

https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#specifying-the-theme-an-image-is-shown-to

It might be better if this action generates light mode and dark mode images and switches between them using the above.