Explicitly create & assign an action slot when importing animation data from BHV and FBX files. Ideally this fix wouldn't be necessary, and it's still my wish to have stronger backward compatibility of the Python API. When/if we have that, this commit could be reverted. Fixes: #131305 Co-authored-by: Philipp Oeser <philipp@blender.org> Pull Request: https://projects.blender.org/blender/blender/pulls/131360 Pull Request: https://projects.blender.org/blender/blender/pulls/131380 Pull Request: https://projects.blender.org/blender/blender/pulls/132549