@metaplex-foundation/umi: Fix react-native serializers dependency export

[ph101pp]

Without this, react-native projects (like Backpack) can't use the @metaplex-foundation/umi package.

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Name	Status	Preview	Comments	Updated (UTC)
umi-docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jun 9, 2024 4:55am

[peterpme]

react-native needs to go first in the exports object

[nhanphan]

thanks for the contribution! - I merged a fix for the tests to the main branch, are you able to pull in the new changes to get passing tests?