Twenty Twenty-One: consistently use theme version when enqueueing resources

[sabernhardt]

previously mentioned on ​PR 10493

Twenty Twenty-One uses wp_get_theme()->get( 'Version' ) for most of its styles and scripts, but three dark mode scripts have a string of 1.0.0.

The string could be changed to modified dates, as Twenty Ten through Twenty Seventeen use for their blocks.css and similar files. However, I prefer making the version consistent within the Twenty Twenty-One theme.

[sabernhardt]

• In ​PR 773, all 4 dark mode resources used '1.0.0' as the version string.
• [49574] switched the stylesheet to
  wp_enqueue_style( 'tt1-dark-mode', $url, array( 'twenty-twenty-one-style' ), wp_get_theme()->get( 'Version' ) ); // @phpstan-ignore-line. Version is always a string.

[SergeyBiryukov]

In 61500:

Twenty Twenty-One: Consistently use theme version when enqueueing resources.

Follow-up to [49478], [49574].

Props sabernhardt.
Fixes #64526.