test: add a test to ensure that "&" is handled equally

[layershifter]

This PR adds a test to ensure that :hover & &:hover handled equally and will work in consistently in style overrides.

[github-actions[bot]]

📊 Bundle size report

Unchanged fixtures

Package & Exports	Size (minified/GZIP)
core makeStyles + mergeClasses (build time)	1.8 kB 861 B
core makeStyles + mergeClasses (runtime)	20.339 kB 7.598 kB
react __css + mergeClasses (build time)	1.837 kB 857 B
react __styles + mergeClasses (build time)	3.535 kB 1.595 kB
react makeStaticStyles (runtime)	8.982 kB 3.908 kB
react makeStyles + mergeClasses (runtime)	22.099 kB 8.317 kB

_{🤖 This report was generated against b699b09ca395e3024ca54c23af873b05421bf41e}