move @types/ dependencies to devDependencies

[todor-a]

Description
I was exploring a dependency graph and noticed that slate-react was depending on two @types packages.

Checks

• The new code matches the existing patterns and styles.
• The tests pass with yarn test.
• The linter passes with yarn lint. (Fix errors with yarn fix.)
• The relevant examples still work. (Run examples with yarn start.)
• You've added a changeset if changing functionality. (Add one with yarn changeset add.)

[changeset-bot]

⚠️ No Changeset found

Latest commit: 2306207

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[todor-a]

@dylans not sure if I should be able to merge this but I can't.