Rollup merge of #130551 - nnethercote:fix-break-last-token, r=petrochenkov

Fix `break_last_token`.

It currently doesn't handle the three-char tokens `>>=` and `<<=` correctly. These can be broken twice, resulting in three individual tokens. This is a latent bug that currently doesn't cause any problems, but does cause problems for #124141, because that PR increases the usage of lazy token streams.

r? `@petrochenkov`

Author: workingjubilee