Fix TokenType comparison logic

[ngocnhan-tran1996]

Closes gh-19377

[DragonFSKY]

Thanks for working on this. One small gap: BearerTokenAuthentication.Builder#token still uses the same reference comparison against OAuth2AccessToken.TokenType.BEARER, so authentication.toBuilder().token(new OAuth2AccessToken(new OAuth2AccessToken.TokenType("Bearer"), ...)).build() would still fail even after the constructor path is fixed.

I think this PR should update that builder check to OAuth2AccessToken.TokenType.BEARER.equals(token.getTokenType()) as well, with a small builder-path regression test.

[DragonFSKY]

Thanks for updating it.