Created by: erengy
Before fc3f4b67, $input-border-color was set to $gray-400. It is now set to var(--bs-border-color) instead, which returns $gray-300. You can see the slight change by comparing v5.2 docs to v5.3 docs, or in the following GIF:
I imagine this change was intentional, as #35857 specifically mentions using a global border-color. In that case, we should remove the comment, as this PR does, to avoid confusion.
Otherwise, $input-border-color should be set to another custom property that translates to $gray-400 as before.
See also #37835 for a similar, recently merged PR.