[ts] Add asserts: false to TSTypePredicate node

[sosukesuzuki]

Q	A
Fixed Issues?	N/A
Patch: Bug Fix?	Y
Major: Breaking Change?	N
Minor: New Feature?	N
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

When babel-parser parses asserts function, it attach asserts: true to TSTypePredicate.

However, when parsing the normal type predication function, it doesn't attach asserts: false to TSTypePredicate.

typescript-eslint/typescript-estree adds asserts: true/false to both. This PR aligns AST for Babel and typescript-estree. (ref: https://github.com/typescript-eslint/typescript-eslint/blob/c41dbe56e0514846e4d21fc5fcd8847da50e92c6/packages/typescript-estree/tests/ast-alignment/utils.ts#L259-L268)

Please close this PR if the current behavior is intentional:smile:

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/29855/

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[nicolo-ribaudo]

Thanks!