Fix Playwright install step

The Playwright install step run in the `test-storybook` job has been
updated to ensure that we are running the correct install command.
Previously we were using `yarn dlx`, which would use the latest version
of `Playwright` rather than the one currently installed. Instead now we
are using `yarn exec`, which will invoke the `playwright` binary from
the locally installed package. This binary has an `install` command
that completes the necessary setup, which is to install custom patched
browsers for Playwright to run.

.circleci/config.yml

@@ -524,7 +524,7 @@ jobs:
           at: .
       - run:
           name: Install Playwright browsers
-          command: yarn dlx playwright install
+          command: yarn exec playwright install
       - run:
           name: Test Storybook
           command: yarn test-storybook:ci