Dependency.expand: ensure pop stack
Dependency.expand: ensure pop stack

During the dependencies expansion, there may be errors (e.g. FormulaUnavaiableError).
As result, some deps will be left behind in the stack and interfere afterwards
dependencies expansion.

So let's ensure stack clean for each expansions.

Fixes #48834.

filcab/homebrew,filcab/homebrew,filcab/homebrew,filcab/homebrew