[css-anchor-position-1] Tests with anchor attribute should change or be marked tentative

[fantasai]

The anchor attribute proposal is not accepted yet, so these tests should either be marked tentative or rewritten to not use the anchor attribute:

• https://wpt.live/css/css-anchor-position/anchor-transition-attr.html
• https://wpt.live/css/css-anchor-position/position-area-scroll-adjust.html

I think the first one is really about the anchor attribute, so should mark it as tentative. The second one though... can it be rewritten to do without? Its metadata seems to indicate it's not about the anchor attribute per se. Or if it's about both the anchor attribute and something else, then maybe we can split the two concepts and have two tests. CC @lilles

[lilles]

https://chromium-review.googlesource.com/c/chromium/src/+/6646507