Add DEFNA as a bronze sponsor

[kjaymiller]

On https://blackpythondevs.com/leadership-summit-2024/ - We need to add DEFNA's Logo as a silver sponsor

[Ngazetungue]

Can you assign this to me

[kjaymiller]

Go for it. you can probably merge this change with #422

[Ngazetungue]

Defa logo added. Added the same time as psf logo. The commit message mistakenly is the same.

[TimOsahenru]

#422 (comment) and this too as well. Thanks