Add LambdaTest to BACKERS.md

[skip ci]

BACKERS.md

@@ -5,10 +5,12 @@ This is a list of all the people who are contributing financially to Panda3D.  I
 ## Bronze Sponsors
 
 [<img src="https://www.panda3d.org/wp-content/uploads/2024/08/Route4MeLogo1185x300-2-1-1024x259.png" alt="Route4Me" height="48">](https://route4me.com/)
+[<img src="https://www.lambdatest.com/blue-logo.png" alt="LambdaTest" height="48">](https://www.lambdatest.com/?utm_source=panda3d&utm_medium=sponsor)
 
 * [Daniel Stokes](https://opencollective.com/daniel-stokes)
 * [David Rose](https://opencollective.com/david-rose)
 * [Route4Me](https://route4me.com/)
+* [LambdaTest](https://www.lambdatest.com/?utm_source=panda3d&utm_medium=sponsor)
 
 ## Benefactors