Enable Playwright forbidOnly in CI to catch accidental `test.only` (#12762)

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

playwright.config.ts

@@ -42,4 +42,5 @@ export default defineConfig({
     reporter: process.env.CI ? [["blob"], ["github"]] : [["html", { outputFolder: "playwright/html-report" }]],
     snapshotDir: "playwright/snapshots",
     snapshotPathTemplate: "{snapshotDir}/{testFilePath}/{arg}-{platform}{ext}",
+    forbidOnly: !!process.env.CI,
 });