`position-anchor` should have an initial value of `normal`

[mkrause]

As per the test here, position-anchor is assumed to have an initial value of none:

https://github.com/web-platform-tests/wpt/blob/master/css/css-anchor-position/position-anchor-basics.html

But in the latest version of the spec the initial value is defined as normal: https://www.w3.org/TR/css-anchor-position-1/#position-anchor

This was resolved on Jan 21, see: w3c/csswg-drafts#13067 (comment)

Relevant comment explaining the current state of things:

web-platform-dx/web-features#3558 (comment)

Should we update the test to reflect the latest version of the spec?