fix(tests): wait until the browser has left the idp before returning from idp_login

Leaving the login page is not enough: keycloak's SAML flow returns an
auto-submitting interstitial on the idp host, and the POST it fires is what
actually creates the user in signoz. Returning at the interstitial let tests
query the user before the callback ran — flaky "user not found" in
test_idp_initiated_saml_authn.

Compare hosts instead of full URLs: intra-keycloak hops (login-actions, the
interstitial, a re-rendered form on bad credentials) keep waiting; the wait
ends only once signoz has handled the callback and redirected.

tests/fixtures/idp.py

@@ -7,6 +7,7 @@ import pytest
 import requests
 from keycloak import KeycloakAdmin
 from selenium import webdriver
+from selenium.common.exceptions import WebDriverException
 from selenium.webdriver.common.by import By
 from selenium.webdriver.support import expected_conditions as EC
 from selenium.webdriver.support.wait import WebDriverWait
@@ -370,11 +371,20 @@ def idp_login(driver: webdriver.Chrome) -> Callable[[str, str], None]:
         password_field.send_keys(password)
 
         # Click the login button
+        idp_host = urlparse(driver.current_url).netloc
         login_button = wait.until(EC.element_to_be_clickable((By.ID, "kc-login")))
         login_button.click()
 
-        # Wait till kc-login element has vanished from the page, which means that a redirection is taking place.
-        wait.until(EC.invisibility_of_element((By.ID, "kc-login")))
+        # Wait till the browser has left the idp host — not just the login page: keycloak's SAML flow inserts an
+        # auto-submitting interstitial on the idp whose POST is what creates the user in signoz. The button is
+        # re-queried per poll; a mid-navigation WebDriverException (detached node) just retries the poll.
+        def _left_idp(drv: webdriver.Chrome) -> bool:
+            try:
+                return urlparse(drv.current_url).netloc != idp_host and not drv.find_elements(By.ID, "kc-login")
+            except WebDriverException:
+                return False
+
+        wait.until(_left_idp)
 
     return _idp_login