Incomplete union function types fixer doesn't wrap original function in parenthesis

[JoshuaKGoldberg]

🐛 Bug Report

• TypeStat version: 0.4.1
• TypeScript version: 4.1.2
• Node version: N/A

Actual Behavior

- let returnsEither: () => string;
+ let returnsEither: () => string | (() => number);

returnsEither = () => "";
returnsEither = () => 7;

Expected Behavior

The () => string should be wrapped in () too.

Reproduction

See ☝️