feat: launch Gemini 3 in Gemini CLI 🚀🚀🚀 (#13279)

Co-authored-by: Adam Weidman <65992621+adamfweidman@users.noreply.github.com>
Co-authored-by: Sehoon Shon <sshon@google.com>
Co-authored-by: Adib234 <30782825+Adib234@users.noreply.github.com>
Co-authored-by: Sandy Tao <sandytao520@icloud.com>
Co-authored-by: Abhi <43648792+abhipatel12@users.noreply.github.com>
Co-authored-by: Aishanee Shah <aishaneeshah@gmail.com>
Co-authored-by: gemini-cli-robot <gemini-cli-robot@google.com>
Co-authored-by: Gal Zahavi <38544478+galz10@users.noreply.github.com>
Co-authored-by: Jacob Richman <jacob314@gmail.com>
Co-authored-by: joshualitt <joshualitt@google.com>
Co-authored-by: Jenna Inouye <jinouye@google.com>

integration-tests/test-helper.ts

@@ -308,6 +308,7 @@ export class TestRig {
         // Nightly releases sometimes becomes out of sync with local code and
         // triggers auto-update, which causes tests to fail.
         disableAutoUpdate: true,
+        previewFeatures: false,
       },
       telemetry: {
         enabled: true,