[themeadapter-material] Fix typo in themeadapter-material.md

[noyize]

No description provided.

[google-cla]

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[bentrengrove]

Thanks for this, you'll just need to follow the instructions above to fill out a license agreement before I can merge it.

[noyize]

Thanks for this, you'll just need to follow the instructions above to fill out a license agreement before I can merge it.

Already signed the CLA