[flame_3d] Fix unrelated broken tests on main due to bug on drawRawAtlas

[luanpotter]

What happened?

The tests flagged on this PR do not work on Flutter main.
That has nothing to do with Flame 3D but it is breaking our build.

What do you expect?

Tests to pass.

How can we reproduce this?

No response

What steps should take to fix this?

No response

Do have an example of where the bug occurs?

No response

Relevant log output

No response

Execute in a terminal and put output into the code block below

Output of: flutter doctor -v

Affected platforms

All

Other information

No response

Are you interested in working on a PR for this?

• I want to work on this