Use number_format() instead of round() on ByteSizeMarkup::create()

Proposed patch to fix fix the problem.

Issue summary is incomplete

Should include the full summary template, with steps to reproduce

Also all fixes should be in MRs and as a bug will need test coverage.

I couldn't replicate this. I tested this as follows, in the CLI with `drush php`:

> \Drupal\Core\StringTranslation\ByteSizeMarkup::create(932023);
= Drupal\Core\StringTranslation\TranslatableMarkup {#7510
    markup: "910.18 KB",
  }