break apart github actions jobs to save disk space

[AdamKing0126]

The Github Action checks out the vagov-content, content-build, and vets-website repos. This is possibly why we are seeing the actions failing with a failure that there's no space left on the device.

The filesystem is preserved between steps in a GitHub Actions workflow. This means that files and directories created in one step are available in subsequent steps. However, the total amount of disk space available in the runner environment is limited. Because we have one action which both fetches the cache and does a yarn install, it's likely this is running against the boundaries for the amount of disk space available.

By splitting this command:
cd content-build && cp .env.example .env && yarn --frozen-lockfile --prefer-offline && yarn fetch-drupal-cache && yarn build

...into three separate chunks:

• cd content-build && cp .env.example .env && yarn --frozen-lockfile --prefer-offline
• cd content-build && yarn fetch-drupal-cache
• cd content-build && yarn build

We should avoid this problem