block-calendar: Use 400 as a valid font-weight

[ntwb]

Description

Reported via #WP47881:

W3C CSS Validator results for .wp-block-calendar table th in wp-includes/css/dist/block-library/style.min.css?ver=5.2.2:

Value Error : font-weight 440 is not a font-weight

Standart font-weight property: [https://www.w3.org/TR/2018/REC-css-fonts-3-20180920/#font-weight-prop]

How has this been tested?

Screenshots

Types of changes

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.

[brentswisher]

This looks good, thank you! I checked and I cannot see any visual difference between 400 and 440 weight, so I am thinking the value likely got set to 440 as a typo more than an intentional choice. @jorgefilipecosta was the original developer on this block - unless he sees some reason not to I will merge later this week.

Possibly worth noting that CSS Fonts Level 4 extends the syntax to accept any number between 1 and 1000 https://developer.mozilla.org/en-US/docs/Web/CSS/font-weight but I don't think that this needs to be set to 440 regardless.

[brentswisher]

I went ahead and merged this, thanks again @ntwb for the work!