The last line of output (which is not terminated by a newline) was not
showing for me when running the merge script. We can either fix it by
specifying `flush=True` at the `print` statement, or flushing before
reading user input. The latter seems more future-proof.

R=machenbach@chromium.org

Change-Id: I61cb929d2f7cdd20b3e32b9beb1653fe2d5c5791
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3676857Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80890}