Expanded animation does not pick up keyframes reference

__Expected behavior:__
Using the expanded `animation` syntax would work with keyframe references.

__Describe the bug:__
Using `{ animation: { name: '$reference' } }` does not replace `$reference` with the related `@keyframes` name, whereas `{ animationName: '$reference' }` does.

__Codesandbox link:__
https://codesandbox.io/s/jss-nested-expand-keyframes-repro-tykpv

__Versions:__
- jss: 10.4.0
- Browser: Chrome 85
- OS: macOS

Start with the CodeSandbox reproduction linked in the issue and trace how expanded animation objects are processed compared with animationName. Confirm the difference between { animation: { name: '$reference' } } and { animationName: '$reference' }. Done means the expanded syntax resolves the keyframes reference consistently with animationName, with the behavior verified against the reproduction.

Written by the indexing model from the issue text.