[css-anchor-position-1] Replace `break-before: column` usage in anchor-position-multicol-011.html

[aethanyc]

Test List

https://wpt.live/css/css-anchor-position/anchor-position-multicol-011.html

Rationale

anchor-position-multicol-011.html uses break-before: column only to push the block containing anchor-name:--foo; into column 2 of #mc. However, Firefox does not implement break-before property yet (Bug 1840944). Since support for break-before is unrelated to anchor positioning interop, I propose replacing it with an in-flow element that fills column 1 to produce the same effect.

[aethanyc]

web-platform-tests/wpt#59294 implements the proposal.