Use "There are no" text in log output when attempting to download YouTube subtitles or thumbnails for a video without them

[synthead]

Simple grammar fix in log output for YouTube when no subtitles exist for requested languages, and when attempting to download thumbnails when thumbnails aren't present.

Before:

[info] There's no subtitles for the requested languages

After:

[info] There are no subtitles for the requested languages

"There's" is a contraction for "there is," and "there is no subtitles" is not correct, as "is" is singular.

Fixes #6726

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[pukkandan]

Same for thumbnails

[synthead]

Same for thumbnails

@pukkandan, are you suggesting to also fix possible grammar issues for thumbnails as a part of this PR?

[pukkandan]

Yes. The same sentence is used for thumbnails and description. For description, it makes sense since there is only one. Since you are fixing subs, fix thumbs too.

[synthead]

@pukkandan, I included a grammar fix for thumbnails and updated this PR's title and body to reflect the changes 👍

[synthead]

Hi @pukkandan! Are there any other changes you'd like me to add to this PR? Thanks!