infra: Sync devcontainer.json and compose file mount location (#20461)
**Sync the config in `devcontainer.json` and `docker-compose.yml`**
Issue: when opening the current `master` branch in a dev container in VS
Code, I get the following message as VS Code cannot find the mounted
source folder:

Opening in a GitHub Codespace works (it seems to ignore the mounts in
the `docker-compose.yml`.
This PR updates the mount in `docker-compose.yml` and the config in
`devcontainer.json` so that the two align.
I have tested these changes in GitHub Codespaces and a VS Code dev
container and both loaded successfully.
Co-authored-by: Bagatur <22008038+baskaryan@users.noreply.github.com>