[2.9.x] Update changed assets in subprojects (backport #12721) by @mkurz

[mergify]

Fixes

• Asset changes in subprojects #12484
• Issue with sbt-web/sassify, sub-projects, and the Play dev server... #12636

To confirm the problem, I first push a scripted test that will fail without the fix from

• If WebJar version is a "-snapshot", overwrite existing files when extracting webjars/webjars-locator-core#159

  ---

  This is an automatic backport of pull request Update changed assets in subprojects #12721 done by Mergify.

[mergify]

Cherry-pick of 6b295a3 has failed:

On branch mergify/bp/2.9.x/pr-12721
Your branch is ahead of 'origin/2.9.x' by 1 commit.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit 6b295a3dd7.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   project/Dependencies.scala

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally