Add GitHub workflow to run tests for changes under loop/webui/...  (#7)

* Add GitHub workflow for loop/webui tests

This workflow runs npm test in the loop/webui directory
when there are changes to files in that directory.

Co-Authored-By: sketch

* webui: use terser output on ci
diff --git a/loop/webui/playwright-ct.config.ts b/loop/webui/playwright-ct.config.ts
index 9c581c4..0dbaa1e 100644
--- a/loop/webui/playwright-ct.config.ts
+++ b/loop/webui/playwright-ct.config.ts
@@ -18,7 +18,7 @@
   /* Opt out of parallel tests on CI. */
   workers: process.env.CI ? 1 : undefined,
   /* Reporter to use. See https://playwright.dev/docs/test-reporters */
-  reporter: 'html',
+  reporter: process.env.CI ? 'dot' : 'list',
   /* Shared settings for all the projects below. See https://playwright.dev/docs/api/class-testoptions. */
   use: {
     /* Collect trace when retrying the failed test. See https://playwright.dev/docs/trace-viewer */