ci: add tinify for png

[c2tz]

Is your feature request related to a problem? Please describe.
No

Describe the solution you'd like
There is this action for minify the png in the folder assets/img i can use this :
Action Tinify

Describe alternatives you've considered
I can also try to use an other recent format like .webp

Additional context
Look the readme.md

[c2tz]

there is also an add on with mkdocs material i should look that more far