Improve the "Auto-update update" text

[johnbillion]

When an auto-update to a plugin or theme is pending, the following text is shown alongside the plugin or theme:

Auto-update update scheduled in X hours.

Note the double occurrence of the word "update". Let's try to improve this to remove the duplication. I recommend switching to Automatic update scheduled in X hours.

The other phrases in the wp_get_auto_update_message() function should be changed accordingly.

[apedog]

+1 for using "automatic updates" instead of "auto-updates" in documentation.
I think the shorthand hyphenated "Auto-Updates" only works when used as a proper name (ie. in titles, in the ui - enable/disable string etc.)

[burhandodhy]

As johnbillion recommended

[SergeyBiryukov]

In 48202:

Security: Improve the wording of messages in wp_get_auto_update_message().

Props burhandodhy, johnbillion, apedog.
Fixes #50489.