build(slic-stack.yml) set the PLAYWRIGHT_BROWSERS_PATH env var

By default Playwright will place browsers used in testing in the
`$HOME/.cache/ms-playwright` directory. Since the installation of the
browser dependencies and the browser must happen as the `root` user,
this would place the browsers in the `/root/.cache/ms-playwright`
directory. This update fixes the path to the one the `slic` user would
naturally use, making it possible to install the browsers as the `root`
user in a location where the `slic` user will find and be able to use
them.

slic-stack.yml

@@ -180,6 +180,8 @@ services:
       COLUMNS: "${COLUMNS:-80}"
       # Explicitly set the env var that will define the Function Mocker cache path: it will be picked up by the config file.
       FUNCTION_MOCKER_CACHE_PATH: "/cache"
+      # Explicitly set the path to the Playwright browsers cache to make sure it will be the same for all users.
+      PLAYWRIGHT_BROWSERS_PATH: "/home/slic/.cache/ms-playwright"
     volumes:
       # Paths are relative to the directory that contains this file, NOT the current working directory.
       # Share the WordPress core installation files in the `_wordpress` directory.