Build/Test Tools: Move the Memcached container into the Docker Compose config.

This allows a developer to use the persistent Memcached object cache on their local development environment via the `LOCAL_PHP_MEMCACHED` environment variable.

Enable the memcached config via `LOCAL_PHP_MEMCACHED=true` in the `.env` file and then restart the environment with `npm run env:restart`.

Fixes #55700


git-svn-id: https://develop.svn.wordpress.org/trunk@53895 602fd350-edb4-49c9-b593-d223f7449a82

.github/workflows/phpunit-tests.yml

@@ -46,7 +46,6 @@ jobs:
   # - Installs Composer dependencies.
   # - Logs Docker debug information (about the Docker installation within the runner).
   # - Starts the WordPress Docker container.
-  # - Starts the Memcached server after the Docker network has been created (if desired).
   # - Logs general debug information about the runner.
   # - Logs the running Docker containers.
   # - Logs debug information from inside the WordPress Docker container.
@@ -159,13 +158,6 @@ jobs:
         run: |
           npm run env:start
 
-      # The memcached server needs to start after the Docker network has been set up with `npm run env:start`.
-      - name: Start the Memcached server.
-        if: ${{ matrix.memcached }}
-        run: |
-          cp tests/phpunit/includes/object-cache.php src/wp-content/object-cache.php
-          docker run --name memcached --net $(basename "$PWD")_wpdevnet -d memcached
-
       - name: General debug information
         run: |
           npm --version